Tohru Honda from Fruits Basket starts out like this. She constantly apologizes for the smallest of things, rarely stands up for herself, often chooses to belittle or instantly forgive very serious wrongs done to her, and is very much a Pollyanna. Much of the series centers around Tohru steadily gaining the courage to face herself and her problems and to defend what she loves.
Hatsumi from Hot Gimmick is so spineless she nearly defines this trope.
A spoilery example to back that up: Hatsumi is so spectacularly doormat-like that she actually apologizes to a guy while he's having her gang-raped by his friends. She's apologizing because of something her father did to the gang-rapist's mother, which prompted the gang-rapist to attack Hatsumi as a form of proxy revenge. I repeat: She's apologizing to her rapist for something she didn't even do. The cherry on top: we later find out that it was someone else's father who wronged the gang-rapist's mother, not Hatsumi's. The whole thing was a Shaggy Dog Story.
Haji from Blood+ is characterized entirely by his complete devotion to Saya and his obedience to her wishes, even when she makes him promise to kill her. Her adopted brother Kai finally goads him into expressing his Bodyguard Crush at the end of the series.
Anthy from Revolutionary Girl Utena is actually described as being "less forceful than a doormat", but the truth is a bit different. She and her brother deliberately play up this trope in order to convince others that their plans for the future are honest, and then to convince themselves that their plans for her are righteous. And her Emotionless Girl act is a result of the massive trauma she's gone through and the way her brother keeps her emotionally anesthetized through their abusive relationship.
Utena herself tries to become one of these in episode 12 to cope with losing a duel to Touga and losing Anthy. Fortunately, Wakaba snaps her out of it.
Nataku in X1999, as it befits him for his nature as a dead little girl's clone.
Nemu from Bleach is a somewhat Rei-like example of the trope. In her case, she was actually created by Mad Scientist Mayuri to serve as his obedient assistant. He has no compunction about injuring or even potentially kill her, as he can simply rebuild her. And yet she still cares for him on some level.
In Code Geass, Karen Stadfeldt/Kouzuki's biological mother, an Eleven maid who was used by an adulterous Britannian, seems to be one of these, which earns her the scorn of the family and disappointment from Kallen's part. Kallen mistook her mom's devotion towards her and her dead brother Naoto as devotion towards the father, and when heartbreakingly proved wrong, she had a change of heart and decided to make Mrs. Kouzuki her reason to keep on fighting, aside of Zero and the Black Knights.
Minor character Miya from Mai-Otome is an unhappy and unwilling accomplice to all of Tomoe's misdeeds, but is afraid to stand up to her. She ultimately gets blamed for everything and is forced to leave school permanently, never to be seen again.
Mousse of Ranma ˝ but only if Shampoo is doing the walking. In a later manga story: the Mask of Submission is a pair of glasses that causes whoever is seen through them to kneel and grovel, begging to be trod upon. He uses them on Ranma a few times to satisfy his ego, then Shampoo, the girl he is a Stalker with a Crush towards, asked him to stop using them. Upon his initial refusal, she told him he was pathetic for taking advantage of items created to protect those who had no other way to fight off martial artists. Then he deliberately puts them on backwards, so he's the one begging and groveling.
Train from the anime version of Black Cat was this for quite a few episodes during his time in Chronos. Speaking in a monotone, hardly having any opinion on anything, and being quietly wangsty. He was also the strongest assassin in Chronos.
Aoi does have a backbone, when she chooses to use it; otherwise, she would have never resisted her parents, time and time again. On the other hand, Taeko is an Extreme Doormat.
Other possible suspects include minor characters Saionji and Chizuru. Saionji has the excuse that we only see him in his capacity as butler / chauffeur.
The Captain from Hellsing basically follows Major around like a big, quiet dog that doesn't do anything unless commanded to. Which sort of makes sense considering he's a werewolf.
Byaku from Kekkaishi is an example of this trope who is also a Big Bad of a major arc. Having no drive or desires of his own, he spends both his flashback and the main story fulfilling wishes of whatever woman happens to be next to him, no matter how potentially dangerous to him, her and innocent bystanders, not because he loves them or anything, but seemingly because he can't think of anything better to do although manga suggests that he loved Hime after all. This is presented as extremely creepy.
Lala-Ru from Now and Then, Here and There is an Extreme Doormat in all but one respect. She can provide water with the use of her pendant, which is an invaluable ability in her desert planet... so much so that wars have been fought over her, often civil wars. She has thus retreated into extreme stoicism and refuses to give anyone water when told, since it just causes death. In this regard, she is more steely than an iron mine, taking heaps of abuse and threats (and implied rape) rather than give in. By the series' end, she becomes a Defrosting Ice Queen and Mama Bear, using her power to help save Sho and her loved ones. Super ending spoiler: she even makes a Heroic Sacrifice to fill the planet with oceans.
Abelia is also this towards King Hamdo for most of the series. No matter how much he shrieks and rants and raves at her, or how insane/barbaric his orders, she quietly carries out his instructions and never, ever speaks back or shows signs of being disgruntled. She gets over it.
Hong Long from Mobile Suit Gundam 00 is a prime example. Not only does he suffer from being the less desired child in his family, but he spends his time taking Wang Liu Mei's abuse and criticism without resentment. The ultimate example of this is at the end of his run where, after they escape the destruction of the Trinity Mothership, they are cornered by Nena Trinity, who has grown tired of being treated as a utility by Liu Mei. As she plans to put a bullet in her, Hong Long takes the shot... and another, and another. Pushing Liu Mei out of harm's way and telling her to live, he confronts Nena... and gets a bullet in his head for his troubles. Not only does Liu Mei not appreciate it, but Nena STILL gets her revenge.
Justified because she remembers how Precia treated Alicia, and doesn't know that those aren't her memories.
Soushi of Inu X Boku SS, who became a Professional Butt-Kisser in order to appeal to his higher ups and worm his way to freedom from a life-long house arrest. One of his previous masters noted that he'd willingly do an embarrassing act with with a smile on his face. He's something of a subversion since he uses this tactic to achieve his own ends, but it's also true he assigns so little value to his life that he'd even commit suicide if that was what was wished of him.
Dolls in Darker Than Black are generally this, although some develop the ability to think for themselves to an extent.
Cooro from +Anima. While he has his own opinions and was a Cheerful Child who loves apples, he won't go against anyone's decisions, even if they were made under stress, frustration or stubbornness. While the early chapters pointed it out, it wasn't until the final volume that it was properly addressed.
Skip Beat!: Kyoko, at the beginning when she used to live with Shou.
Honey Hunt: Yura, up until her Abusive Parents divorce and reveal they couldn't care less about her. This results in her first Crowning Moment Of Awesome when she tearfully announces to the press that she no longer considers them her parents and that "people like them should just burn in hell". Even after that though, she still shows instances of this trope at times.
In Monster, Tenma starts off as a complete bitch of his fiancee and his boss, who publishes his research under his own name and takes credit for his extremely difficult surgeries. Although he grows a spine early in the series' run, both his and Eva's flashbacks characterize him as woefully passive and exploitable.
Sawako from Kimi ni Todoke is this normally, but it's subverted when she refuses to help Kurumi get together with Kazehaya, on the basis she can't support her fully due to her own feelings for Kazehaya.
Tsuna from Katekyo Hitman Reborn!, though he gets better somewhat. Kozato Enma even more so. They become fast friends mainly because of how they can relate to each other in this aspect.
SHUFFLE!: After discovering that it was not Rin's fault that her beloved mother died (it was indirectly her fault), Kaede Fuyou becomes a House Wife whose only purpose in life was, according to her, "to serve Rin-kun" so she can make up to him for all the tremendous abuse she piled on Rin (who willingly took the blame because Kaede was this close to just let herself die by despair) before the discovery.
Yukinari Sasaki from Girls Bravo. Granted, he tries to stand up for himself when people bully him but he usually ends up backing down. People mock him for this by saying "You're too much of a coward to talk back! If you're a man then act like one!" Also, he takes frequent beatings from his friend Kirie for being an Accidental Pervert and hardly ever complains to her about it afterwards. He also never decides to say, stop being friends with her and frequently blames himself for when bad things happen to him.
Hinata from Naruto was shown to be one of these during her childhood. Her interactions with Naruto enable her to grow out of it.
Don't forget about Sakura. She's this around Sasuke, especially in Part I. The scene in the hospital shows it quite well, with Sakura not doing anything to call Sasuke out on his actions.
Itachi of all people, fits this trope pretty well, combining it with Well-Intentioned Extremist and My Country, Right or Wrong. What's that, Danzou? You need me to kill my entire clan to prevent a war? No problem! Okay, it's not that simple, but you get the point.
Speaking of Danzo, his ideal of a shinobi leans toward this: An individual with exceptional combat skills, a willingness to die for his country, and no emotions or opinions to prevent him from doing so. He does his best to mold Root in this image but falls short himself, to his own disgust.
Unfortunately for the Shinobi, this is also true for the Daimyo's. They all seem to be pretty spineless, not to mention stupid.. And they're supposed to lead the country?
Anri Sonohara from Durarara!!. She eventually starts to develop a spine.
Also, Saki Mikajima. She'll listen to whatever Izaya tells her to do, even if it means endangering her life. Even after she betrays him, she continues loyally obeying him afterward, too.
Masato and Miku of Zeorymer are both the most doormatty of Extreme Doormats.
Ayumi of Gokinjo Monogatari. When she's chosen as the receptionist at the fashion contest and can't move from the hall, she even gets a comment from Yuusuke, that it suits her just perfectly.
Little House with an Orange Roof: For a tsundere, Natsumi has serious problems saying "no", especially when challenged to "prove" she's worthy to marry Shoutarou. This has led to her being groped by slimy salarymen in a cabaret, and being utilized for slave labor by her in-laws, among other things.
Yukiteru Amano of Mirai Nikki starts out as an Extreme Doormat, and becomes less of one as the series goes on.
Soubi in Loveless. Ritsuka tries to break him out of it, but Seimei would prefer he stay that way.
Kenshin was this during his days as an assassin. He never asked questions, made conversation, or gave his opinion with his superiors who gave him orders to kill. He only did what was necessary to bring on the new era - even if it would cost him his sanity in the end.
Tick Jefferson of Baccano! tells Luck that he'll do anything to prove his worth to them. He'll also do anything that will let him use his scissors.
Lithuania in Axis Powers Hetalia seems to border on this- he's sweet, humble, obedient, and pretty happy considering how much he gets bossed about, esspecially by Bad Boss Russia and best friend Poland.
Arcee in Transformers Headmasters. After being an Action Girl throughout the movie and season 3, she was turned into a docile, subservient secretary, who didn't wield a weapon once in the entire series, and rarely left the "office".
Gilbert Nightray of Pandora Hearts is often this to his master Oz, but with Alice he normally stands up to her.
Tetsuma in Eyeshield 21 is this to his old friend Kid, to the point he is very Literal-Minded and takes orders to the extreme, doing ONLY what Kid told him to do. It was only after Monta defeated him in a catching battle that Tetsuma began to develop his own ambitions and more emotions.
Sanada Yukimura from Gate 7 is so much of a doormat that he's called to shut up by his students...kindergarten students.
Sloth from Fullmetal Alchemist is so lazy, he lacks the basic will to say no to what Father and the other Hommunculi tell him to do.
Rei from Sangatsu No Lion is a bit lacking in the ability to stand up for himself, especially when it comes to Kyoko, who regularly belittles him without receiving complaints and attempts to manipulate him into losing. While he refuses the her worst of her commands, he's never able to completely turn her away and always acquiesces to her smaller (but still generally unreasonable) requests. His narrative heavily implies it's because of his affections toward her.
Gohan from Dragon Ball Z was one for most of the series: a total mama's boy who worked diligently at his studies, whenever Goku wasn't stealing him for more training to save the world. Characterization Marches On, however, and we see him gradually learning to stand up for himself and the people he cares about in the Namek saga, though Vegeta's criticism still got him to clam up. Even when he was a teenager, Videl managed to blackmail him into submission.
Minato Sahashi of Sekirei is this, being beyond humble and completely lacking in confidence. It may be somewhat justified, when one considers the absolutely terrifying women he grew up with.
Bertolt Hoover, from Attack on Titan. He seems to be exceptionally aware of his own failings, and resigned to it even with his exceptional talents as a soldier. However, his claims that he has "no will" of his own and simply goes along with what society expects from him leave absolutely horrifying implications when it's revealed that he is the Colossal Titan and a spy sent to infiltrate and exterminate humanity.
Legato Bluesummers from Trigun wants to be one of these for his master Knives. He even admits in the manga that he has no reason to live without Knives, and eventually he gives up his own life just to torment Vash, whom Knives had ordered to make suffer.
Rei from Neon Genesis Evangelion is one of these. She shown no emotion, carries out any order given to her with absolute obedience, and has no problem being considered completely expendable for the sake of the mission.
One Piece has a minor character named Baby-5. She cannot say no to anyone. Because of this, she's been engaged multiple times, and has a debt in the hundreds of millions. Heck, she even accepted a request from someone she was wanted to kill before!
Keitaro of Love Hina. He constantly lets the girls walk all over him and beat him up, even though as the landlord of the girls dormitory where they live, he could EASILY evict them at any point. In fact, it's ONLY because he's a doormat that the girls still have a roof over their heads!
Insignificus in Secret Six. He does anything a member of the Secret Six says while lamenting that he is not worthy to shine their shoes
When Magneto ran the Brotherhood of Evil Mutants, the doormat role was played by the appropriately named Toad.
X-23, of all people, spent time as one when she was a prostitute under the violently controlling and abusive pimp, Zebra Daddy. She lets him walk all over and control her even though she could tear him to shreds if she wanted to. And eventually she does. To a certain extent she was this when still under the control of the Facility, as well, allowing Rice to subject her to horrific amounts of physical and emotional abuse even though, like Daddy, she could kill him in seconds. And once again, eventually she does. Though not in seconds...
The titular character from the MLP:FiMfanficQuizzical. Overcoming her tendency toward this, if only somewhat, is the point of the story.
Dominic in Pink Personal Hell and Altering Fate shows traces of this. When Pinkie Pie and Gummy (literally!) walk all over him, he doesn't do anything except voice his annoyance. It's implied that he is often this way with other people, becoming a borderline Hikkikomori. Nickel Steel is also this way at first, never leaving the bedroom unless escorted out, constantly thinking he wasn't able to do anything, never speaking to ponies unless introduced, but he starts opening up to others. Revealed to be Dominic's Character Development. Although he still lets Pinkie Pie jump all over him.
Poor Fix-It Felix Jr. from Wreck-It Ralph. He's so much of a Nice Guy, the bystanders he saves on a daily basis from Ralph (in-game) take advantage of his kindness to force him to keep Ralph out of his own 30th anniversary party.
When you think about it, Felix is just as much The Woobie as Ralph. Just in a different way.
Film - Live Action
Titanic: When it comes down to it, this is what Ruth and Cal wanted to turn Rose into. For Ruth, the obedient, well-behaved daughter. For Cal, the perfect little wife who exists to love, obey, and honor him.
In Coming to America, the woman Prince Akeem was to enter an Arranged Marriage was groomed to be an Extreme Doormat, totally compliant to his every whim and wish. Unfortunately, Prince Akeem didn't like the idea of being married to such a woman, and his desire to find a woman with a bit of spine begins the plot of the movie.
Harry in Dumb and Dumber. Throughout the movie, he comes off as a little smarter and more sensible than Lloyd but for the most part goes along with everything Lloyd does partly because he's just very passive.
Larry from The Three Stooges comes across as the most sensible of the three in most of the shorts but apparently only goes along with what the others do and puts up with Moe's abuse because he's just very passive. The fact that Curly and Shemp also put up with Moe's abuse makes them examples of this as well.
Milton in Office Space (up until the very end, at least.) He was compliant every time he was told to move his desk, until he ended up essentially in a closet in the basement (with the light turned out!). That is, until he burns the place down and runs off with the stolen money.
Stu from The Hangover, who allows his girlfriend to abuse him, cheat on him, and boss him around...until he finally stands up to her at the end.
Number Two:NO!(sobbing) I'm sick of you pushing me around!
This is then followed by a Double Subversion: Dr. Evil initially appears remorseful for having made his right-hand man cry, and suddenly adopts a paternal stance, but then he changes his mind and executes Number Two anyway.
Anita Blake: Nathaniel. Until he grew a pairto please his mistress, the title character, he was so incredibly submissive and masochistic both in and out of the sex dungeon that he literally could not do anything without his master's/mistress's permission. Oh, did I mention he's a wereleopard(?!) Nathaniel was probably this way before becoming a wereleopard, having been a child prostitute, raped, and a drug addict, not to mention living in an abusive home before all that. Dominant natures are not created by gaining the ability to shift shape. When you consider he's first introduced at age seventeen or so, and all this has already happened to him... It makes more sense.
Archer's Goon: Quentin, Howard's father, is this; he explicitly states that his role in life is to be a passenger.
The Other Mother really wanted something to love so she tried to keep Coraline for herself and make her into the "perfect, obedient daughter". Such as when she tries to sew buttons on her eyes so that she'll be a well behaved "little doll".
The Other Father is this to the Other Mother. Even though he obviously wants to help Coraline, he is unable to.
Ashley Wilkes, who disagrees with the American Civil War but is willing to fight anyway.
His wife and brother-in-law also fit the trope. Scarlett married Charles partially because he was so biddable to her, and Melanie is subservient to everyone, unless they trigger her Berserk Button by mistreating Scarlett.
The house elves. They seem to share a universal inferiority complex, despite incredible magical power. They live to serve, literally, and seem to be happiest slaving away for their masters, but have extremely powerful magical abilities and are able to defeat powerful wizards without too much difficulty. On the other hand, house elves are shown to be more than capable to skirt around orders or outright attack people if it means protecting a wizard or witch that they really care about. While Dobby was a prominent example, Kreacher was shown putting up a good struggle against the orders of Sirius (his master), just because he didn't like him. And then there's the fact that several hundred house elves - who technically were under control of Death Eaters since Hogwarts was being run by Snape and the Carrows at the time - had no problem rallying together and saving the defenders of Hogwarts.
Of course, since Snape was only running Hogwarts on Dumbledore's request and not for the Death Eaters as everyone believed, the elves probably weren't as controlled by the Death Eaters as appearances suggested.
Played straight with Merope Gaunt; implied with Eileen Prince.
Dobby was a unique case - he was suffering abuse above and beyond what a house-elf would be inclined to expect even from a master like Lucius Malfoy. In a later book he tells Harry that when he was hired by Dumbledore, he actually talked the man down from a very generous salary and vacation package to a pittance with no vacation time. He likes work just fine, the Malfoy family was just that bad.
He got one day off a month with Dumbledore, and even considered that a bit much, from the sound of it.
The Hollows: During the time she had spent with Algaliarept, Ceri seemed to be this. She regained her pride pretty fast, though. That's because she got her soul back. Al had stolen her soul to make her serve him, but Rachel negotiated for it to be returned as part of their deal.
The Host: Wanderer. Even the human colonists eventually get annoyed. Part of this is due to the communal nature of the souls but part of it is a survival strategy to avoid antagonizing her (understandably) hostile captors. She gets better about it as she feels less threatened.
In Death series: Purity in Death reveals that Donald Dukes's wife is this. She knows what he's doing and seems unable or unwilling to do much about it. Eve Dallas, considering her Dark and Troubled Past, has little patience for people like this.
Bertie of this P. G. Wodehouse book is the epitome of this—story after story shows that he can be bullied or cajoled into anything. He suffers the worst of one Zany Scheme after another because he's simply unable to say "no" to a friend, Jerk Ass or otherwise. Besides that, he's afraid to stand up to his Grande Dame aunt, and he lets his valet dictate every facet of his existence, even down to the details of his wardrobe. Attempts to assert his rights by keeping an article of clothing Jeeves disapproves of invariably give out by the end of the story:
Anybody can talk me round. If I were in a Trappist monastery, the first thing that would happen would be that some smooth performer would lure me into some frightful idiocy against my better judgment by means of the deaf-and-dumb language.
Another Wodehouse example is "Corky" Corcoran, who lets himself get dragged into all sorts of schemes by his friend Stanley Ukridge.
Kushiel's Legacy: Phedre isn't this, but she acts like it when working in her professional capacity to satisfy the unique tastes of her clients. More than one enemy, up to and including a God of Evil, has failed to recognize the difference until it was too late.
Malory Towers: Catherine from this series. However, the other characters dislike her strongly because she's always so kind and friendly and helpful- for instance, she once sharpened all of Belinda's pencils for her without asking. However, Belinda used them for her art and kept some of them blunt on purpose, and so she definitely didn't thank her. They nickname her 'Saint Catherine' at one point and use it mockingly.
The Manchurian Candidate: Raymond Shaw, although he is too arrogant to be a perfect fit, has many of the features of this. He has little drive or emotional depth, and he always caves in to his shrewish mother, even giving up the only girl he ever had any interest in just to shut her up.
Mansfield Park: Fanny Price becomes this after living 8 years with her neglectful Aunt and Uncle Bertram and her aunt Mrs. Norris. This makes the moments where she stands up for herself, such as refusing to marry The Casanova, all the more impressive... and astonishing to her fellow characters.
Oblomov: Agafya. The titular character is also guilty of this, seeing as he is pushed around by Tarantyev.
Shoeless Joe: Annie Kinsella: Her main line of dialogue is "Oh love, if it makes you happy, you should do it," even if that means Ray should plow up his crop and build a baseball field and then kidnap J.D. Salinger on a whim, risking financial ruin and jail time. Averted Trope in the book's movie adaptation, Field of Dreams, in that Annie also receives a few of Ray's visions herself.
Sourcery: Coin is a Tykebomb who effectively grew up possessed. He's never made his own decisions in his entire life, so he never learned how.
The Stranger: Mersault thinks that nothing really matters, so he does pretty much anything people ask him to.
The Ties That Bind: Laika qualifies if she took corporal punishment for 20 years without complaint and willingly became a slave in BDSM.
Unseen Academicals: Nutt is basically this, and it's repeatedly given more than one Lampshade Hanging. He's described as an "amiable milksop", and tries to always be helpful and agreeable and "accumulate worth" because he's an orc and was at worst horribly abused and at best taught to keep his head down as a survival strategy. He does have opinions, and sometimes expresses them, but is very meek about talking to anyone he doesn't know well.
Phenix from Of Fear and Faith is this with women, although he is slightly more assertive around his own gender.
In Vorkosigan Saga Ivan Vorpatril is a subversion. At first he'll do almost anything Miles says(with proper amounts of grumbling of course). Later he learns to show some initiative.
The main villain in Twistaplot #12: Journey to Vernico 5 had turning practically everybody in the universe into one as his goal, only he prettied it up by calling them "Willingness Workers."
Simona Ahrnstedt gives us Sofia Löwenström her debut novel Överenskommelser. Fearing that she would get beaten by her abusive father, she hardly ever expresses any opinion of her own. So people are really astounded if she does. Sadly enough, her mother has become this as well because of her abusive husband.
Venus Dag och Natt in "De skandalösa" is also very close to this. She's so desperate to please her mother and doesn't seem to have any opinions of her own.
Live Action TV
Supernatural: When it comes to his family, Dean is so like this it's scary. He thinks he deserves the verbal abuse or blame from just about anybody, and is so needy when it comes to Sam that he sells his soul to bring Sam back from the dead. He's saved from living here by being opinionated and obstinate in everything else.
In "Hunted" he's kidnapped and used as bait after Sam just abandoned him in the middle of the night, pretty much dismissed him with a "He means well," and didn't contact him until he needed him. And all Dean can come up with is a "You ever do that again and I'll...". Do what, Dean? Grow some spine when it comes to dealing with your family?
In season four, Sam stops just short of choking Dean to death after Dean calls him a monster on top of Sam's hallucinations of Dean loathing him in one episode. Guess who calls to apologize to whom. Of course, that might be as much practicality, since Dean needed to get Sam to go to back to Bobby's to continue the incredibly painful process of detox. Or at least stop following Ruby's plan. His apology probably would have had the desired effect, too, if the angels hadn't meddled with the message.
It gets so much worse in Seasons 5 and 6. No wonder Famine accused him of being empty: he's got nothing left to give, not even to Lisa and Ben, because he's given it all to his family, who never needed him as much as he needed them.
Angels are implied to supposed to be this—follow your orders and don't ask questions—and the higher-ups don't like it when the doormats start questioning.
Castiel can also be an Extreme Doormat, although Depending on the Writer and his mood, sometimes he just straight out rebels and loses his shit. During his breakdown in season five, he tends to sacrifice himself and obey the Winchesters (particularly Dean) without question, no matter how much it hurts him. Castiel is even reduced in rank and tortured by heaven because he is getting too emotionally attached. A physically and psychologically broken Cas takes on all the damage a time travel trip requires (to the point that he cannot stand up), in order to make sure Sam and Dean survive. Given how readily and unquestioningly the millenia-old Cas sides with Dean, and Castiel's (obviously untrue) claims about Angels not having emotions, it's likely that he was just so eager to have someone he could believe in telling him what to do that he so willingly switched from being heaven's doormat/bitch to being Dean's doormat/bitch.
Lord Percy in Blackadder is like this. He sticks by Blackadder whenever he's in trouble, offering to pay his debt, creating gold (or in this case green) and posing for a less than wholesome portrait for his friend; while all the while Blackadder steals his money, insults him and takes advantage of his generosity all the way through the series and Percy does nothing to complain.
The Actives on Dollhouse are pretty much like this when in "blank slate" mode. They act like Purity Sues except even more obliging and unambitious. They're basically like children on Valium.
Darryl Morris on Charmed has done everything for the Charmed Ones. He even forgave them after Phoebe and Paige stole his soul. He had managed to grow a spine after getting put through the wringer one too many times without a thank you and put some distance between him and the girls. They didn't understand why.
Played with in The Fast Show. One of Paul Whitehouse's characters tries to have opinions about the topic du jour whilst talking with his mates in the pub, but refuses to disagree with any of them for fear of offending. As a result he fails to come to a conclusion about anything and lives his life in a state or perpetual bewilderment.
In a Monty Python sketch, a couple goes to marriage counseling. The counselor instantly seduces the wife right in front of the husband, who can't bring himself to utter a word of protest.
Jerry on Parks and Recreation. He's constantly the butt of jokes and barbs from everyone in the office, even the nicer co-workers, and he rarely objects with anything more than an exasperated sigh.
Niles Crane on Frasier was portrayed as this, at least to his wifeMaris, almost completely ignoring the fact that she treated him like crap and running to her pretty much whenever she snapped her fingers. He got better about this tendency over the years, eventually culminating in his divorce from Maris and learning to be on his own.
In a Flash Back episode of Taxi, we discover that no one else than Jim Ignatowski was this during his days at Harvard, "a simpler time" in his own words.
In an episode of Star Trek: The Next Generation it's revealed that Jean-Luc Picard has an artificial heart because back when he was at Starfleet academy he got in a fight with a group of Nausicaans and got stabbed in the heart, almost killing him. Because he regrets this part of his past life, and especially this event which more or less crippled him for life (at least in the sense that he needs regular checkups on his artificial heart), Q offers him the chance to go back in time and allow him to not fight the Nausicaans. The aesop was, of course, that this was actually a crucial point in his life that shaped his entire career. Without the stabbing that almost cost his life, Picard never realized how fragile life is and how important each moment must be, he never got the motivation, drive and ambition to live life to the fullest and become a great man, and he instead became basically an extreme doormat who never achieved anything of any importance, never taking any risks, always playing it safe and never seizing any opportunities to advance in his career.
Rumplestiltskin from Once Upon a Time. Dear Lord. Crippled (no political correctness about this in Fairytale Land), poor, insulted in public by his wife, insulted in public again by the man she runs off with, deeply humiliated by a soldier in front of his own son and threatened with loosing that same son, ... His inability to fight back is explained to a great part by the fact that he has next to no combat knowledge, is only ever seen walking with the help of a crutch and often up against soldiers backed up by the Dark Onewho are likely to do even worse to him if he speaks up. Still, a conversation with his son implies that in some situations, like the war, fighting is at least possible. Later on of course he gains some power...
Prince Henry is this to his wife Cora and daughter Regina. In "The Miller's Daughter", he does show concern over his father's treatment of peasants but lacks the spine to stand up to him either.
Jiminy Cricket used to be this; unable to stand up to, much less escape, his thieving, sociopathic Jerkass parents. His attempt to use magic to get away ends up getting Gepetto's parents killed. In the end, he is ''more' than glad to trade his humanity to the Blue Fairy and accept a geas to aid Gepetto just to leave them. He's still pretty meek, just don't get between him and his patients.
2-D of the Gorillaz is an Extreme Doormat to Murdoc. To date the psychopathic bassist has kidnapped him, stolen his girlfriend, sold most of his belongings, taken several of his organs, beat him up repeatedly and run over him... twice. And though 2-D has only recently smartened up to this and come to resent Murdoc, he's still too afraid of him to do much.
Caspar Milquetoast from the 1920's comic strip The Timid Soul. His name went into the dictionary as a word for this trope.
Linus Van Pelt is another good example, due to being naturally introverted and to having a dictatorial big sister who is also physically stronger than him. (Actually, Lucy has this effect on lots of men, including Schroeder.)
Linus finally reached his breaking point at the end of a story arc that started when he rashly promised his "blanket-hating" grandmother that he'd stop carrying around his blanket as soon as she stopped smoking, thinking she was too much of an addict to ever quit - and Grandma did just that! After demanding Linus fulfill his end of the bargain and forcibly taking the blanket from him, Lucy spent the next week or so taunting her brother, who was already such a nervous wreck that he was fainting several times a day. Linus went so far as to hire a private detective (Snoopy, who else?) to try to steal the blanket back, but no luck. Grandma finally relieved Linus of his promise after she admitted to him that she had sneaked a cigarette, only for Lucy to not only refuse to give the blanket back, but to claim that Linus had proved he could survive without his blanket and no longer needed it - and that it was time for the blanket to be burned. With Linus following after her and fruitlessly pleading, Lucy took the blanket to a garbage bin (which she lied was actually a furnace) and performed a "liberation" ceremony that ended with her tossing the blanket right into the "furnace." Linus let out an unearthly scream, furiously fished his blanket out of the bin, and then let his bitchy sister have it with all the righteous anger at his disposal.
Linus: Nobody's going to treat me that way anymore! Who do you think you are to tell me what to do? And Grandma, who does she think she is? When Mom tells me I have to give up this blanket, I'll do it, but that doesn't go for anyone else, YOU HEAR ME?!
Slave Mentality in GURPS turns your character into this towards his owner only. If ordered to "make them give you the money and don't take any gruff" a slave mentality character will not hesitate to stand up against the most physically and socialy intimidating person.
Beholden in Genius The Transgression, who lack a worldview of their own and generally end up simply going along with the most convincing Genius in the area and serving the vitally important role of Igor.
Yuna from Final Fantasy X. She apologizes or is sorry for eveyrthing that happens (including being kidnapped and other things that she couldn't prevent or wasn't even concerned in) and triggers a major plot element by accepting Seymour's proposition to marry him despite being fully aware that he is planning to eliminate the council of Yevon because they Guadosmocked him for being a Half-Human Hybrid. Oh, and even after he DIES and comes back as a ghost, she still wants to marry him so she can send him to the Farplane. Justified by her habit to try to do everything by herself without warning so nobody else will be hurt, even if she doesn't seem to realise that her Guardians have to rescue her if her plan fails. And the sole reason she became a Summoner in the first place? Because her father was one and killed Sin via the ritual Heroic Sacrifice, thus giving a few years of peace to Spira, so she has to do the same. The majority of Yuna's Character Development in the game is outgrowing this. The turning point being the moment she confronts Yunalesca and resolves to find a way to end Sin permanently.
To be fair, 358/2 Days takes place at least partly during/immediately after Chain Of Memories, so it makes sense that that Namine's Character Development might not be so clear.
Dragon Quest VII has Pepe, who just wants to keep everyone happy, but is pressured and pushed into a situation where he 'must' choose between his lover Linda and his family... because Linda refuses to do anything to solve her own problems and expects him to sweep her away from it all by eloping, regardless of how that would leave his family to deal with her family's debt. In the end, he cracks under the pressure and leaves town alone. This doesn't help.
Charon, a possible companion in Fallout 3, has been brainwashed to unquestioningly obey whomever holds his employment contract. His doormat behavior doesn't extend to anyone else, though. Employers who antagonize him would be well advised not to fire him.
Yes Man in Fallout: New Vegas is forced to be as helpful as possible due to his programming. However, he's also incredibly cheery about it. If the player decides to kill himnote Don't worry, he'll upload himself to another Securitron all he can do is beg for mercy and say that he deserves it. Of course, he's actually instrumental if the player wants to be the sole ruler of Vegas and in the Independent Ending. He tries to avert this a bit where he states in the ending that he's found an upgrade that lets him be more "assertive", specifically that he'll only take orders from the Courier.
Saori Hasegawa, the Hermit Social Link in Persona 3 Portable's female path. Naturally, she ends up on the receiving stick of some Malicious Slander, and it's up to the protagonist to teach her to enforce her opinions.
Dante Moro in Assassin's Creed II, who is left extremely impressionable after being knifed in the head. The guy who paid the thugs to attack him (who secretly lusted after Moro's wife) is subsequently able to talk Dante into anulling his marriage, and even has the audacity to hire him as a bodyguard.
Uther, leader of the lost kingdom of Insalaum in Super Robot Wars Z2: Saisei-Hen starts out as one of these, taking orders from an old hag of a prime minister, retreating after taking a single hit and just being an all-around sissy. Once he awakens his Sphere, he does a complete 180, gains about fifty levels in badass, smashes the final boss of the first game into the dirt with one hit, and if you end up taking the "If" route, he becomes the game's Big Bad.
Lilli of Edna & Harvey: Harvey’s New Eyes is this by way of Heroic Mime. She never has an option to talk, only to begin a sentence that's then interrupted by another character guessing what she's going to say. Nor, at first, does she have the option to disobey orders given by authority figures. Over the course of the story, she's forced to disobey some people's orders in order to help other people, but the degree to which she develops a spine depends on the ending. If she surrenders to Dr. Marcel, it's all for nothing. If she kills him, she's still doing what the story wants. Only in the semi-hidden "Contradict" ending does she tell everyone, including the Interactive Narrator, to stuff it.
Dehl in The Reconstructionnever acts whenever anyone, mainly Tehgonan insults him. Its only after Havan devastates the world that he becomes assertive, to a huge degree.
Used as a Deconstruction in the Visual NovelHeart De Roommate when one of the girls accuses the resident Yamato Nadeshiko of being this, only coming across as sweet and innocent because she's too much of a moral coward to have her own opinions. Amusingly enough said character quickly proceeds to rectify this by expressing her own opinions on the other girl's Genki Girl / Yandere tendencies. Thus proving that she really was a Yamato Nadeshiko; otherwise she wouldn't have the inner iron to do such a thing.
M in Shikkoku No Sharnoth never shows any emotion or interest in anything. He doesn't even bother telling people to leave him alone.
Assassin in Fate/stay night never varies from polite interest in his emotions. Caster partially ruptures his lungs, he continues chatting. True Assassin eats his way out from inside and he practically comments on the weather. Bleeding to death after Saber has run him through? Talk about birds. He expresses no opinions or goals beyond wanting to have one good fight during his tenure as a temple guardian. He can't leave the temple because he'll vanish if he does, and even if he beats everyone else, his master wins and gets the Grail and he still won't get anything because he is a fake Heroic Spirit that is something of a composite identity, and therefore has no wish to be fulfilled (not that the Grail would grant a wish to fake like him). Why bother?
Also Kuzuki, who weirds out Shirou with his complacence. Around the time Archer kills him, though, it seems like at least SOME of this is faked. Continuing a fight to the death against someone you have no hope against just because he feels he ought to finish what he started? Suuuure.
Ken Krause of Jake Hunter Detective Story: Memories of the Past, with no small amount of lampshading by several characters.
Genji Ronoue from Umineko no Naku Koro ni is "exemplary furniture," according to Ronove. He basically lets Kinzo and Beatrice do whatever they please, even if that includes killing the rest of the family. He even shocks Kanon by passively accepting Beatrice as his new master after she kills Kinzo in the third arc... and her next task for him is to die. He complies.
Clair Vaux of Bernard in Requiem of the golden witch, as she is merely a tool created by Bernkastel for the purpose of reading Beato/Yasu's past.
Kazuo of Red String fits this trope perfectly. His entire life is wrapped up in winning his Father's aproval. From his job, to his major, to the girl he marries he'll do anything Kenta says. Shame Kenta sees Kazuo as worthless and nothing but a bargaining chip, which finally drives Kazuo to attempt suicide.
Kusari from Sluggy Freelance is an interesting case: She does have an attitude, but that's about all. She still obeys the CEO of Hereti-Corp absolutely, and though she is capable of rational, independent thought, she has no motivation to do anything but serve. Mind Control is suspected, but it also seems like she has been made this way from the start and has no "real" self.
Gary from Ménage ŕ 3 allows himself to be beaten, kissed by his gay friend (who is well aware he's straight) and prevented from having sex by the person who claimed she would help achieve this goal.
Marten in Questionable Content indulges a little snarking now and then, but most of the time patiently endures all kinds of crap from the rest of the (mainly female) cast. Oh! And his former job was "office bitch" (with an official office bitch business card, no less).
Tavros in Homestuck, to the point where he can't even bear a grudge towards the person who paralyzed him. Taken to extremes in the afterlife when he can't even bear a grudge towards the person who killed him. Who is the same person who paralyzed him earlier. After another round of verbal abuse from the same person, Tavros finally gets fed up and flies away while flipping her off.
Mituna swings between this and a sort of even more aggressive Karkat mode with poorly spelt profanity.
Helen from Penny and Aggie, who throughout the course of the series had basically been treated as a minion for various cliques—as well as The Unfavorite in her household, who was expected to advertise for her sister, and given a conditional love response for failing to do so—and at one point explicitly thinks, "At least if I'm being used, that means I have a use." Eventually she runs away in response.
Elliot from El Goonish Shive tends to be this when villains aren't involved. It actually causes problems, as his inability to take initiative or make choices based on his own needs basically ruins any romance he's involved in.
"Handy" from Void Dogs doesn't even consider herself to be a person. Considering that her real name is a serial number, this might not be surprising.
Several characters from Tales of MU show levels of doormat affinity, but two in particular have fit the definition of Extreme Doormat:
Two the Golem was set free with an order to do what she wants, but she was created with only one desire: to do as she's told. Her growth out of being an Extreme Doormat began when she learned to have other desires, starting with eating sweets.
The Lizard Folk use communal decision making, so Hissy holds no strong opinions of her own. Human missionaries decided she should go to school, the school decided she should join the skirmish team. Her response to all of it is simply that she has no objection. As a background character, her Extreme Doormat status wasn't even apparent until she got some Character Development.
Weasley Crusher of The Binder of Shame was constantly bullied by the other players, on one occasion being pushed into buying pizza with money he said he needed for insulin.
Although he likes starting arguments, The Nostalgia Critic constantly succumbs to peer pressure because he desperately wants to be loved and those arguments nearly always end with him crumbling for not much reason.
In We Are Our Avatars, modified Asimovian laws mean that a human simply has to give Yuzuki Miura from a command, which she is unable to resist.
Liane Cartman, Eric Cartman's mom. She will give her son anything and everything he wants to ridiculous extremes, without objection.
One episode focused on this, with the Dog Whisperer basically explaining that her social ineptitude means her son is the only real companionship she has, which is why she will do anything to make him happy so she can spend time with him. This is one of the reasons Cartman is such a Jerkass and a spoiled brat.
And in a more recent episode, She finally decided enough was enough and started denying Cartman... only to have him convince everyone that she repeatedly raped him - in public.
Chris from the two-part episode "Do The Handicapped Go To Hell?/Probably" is also an example of this, as he lets the rude/abusive Saddam walk all over him during the episode and reacts very passive-aggressively to Satan cheating on him.
Butters in his pre-breakout days. Though he sometimes sill qualifies when he's not playing the Woobie or Badass Adorable.
MODOK in the animated Iron Man series (from the '90s) has aspects of this trope, constantly putting up with the Mandarin belittling him and even having to be persuaded out of helping him enact a plan that would KILL HIM. When asked why he puts up with it he answers "He makes me laugh. Seriously, I like him."
Wilt from Foster's Home for Imaginary Friends. His catchphrases are "I'm sorry" and "Is that okay?". When lost in the woods, his first suggestion was "I can starve first if it helps."
Occasionally he has outbursts of anger at being treated as a doormat... and then apologizes for it.
Kif Krocker is a more moderate example, justified by having Zapp Branigan as his superior.
Mr. Milk from Making Fiends has quite a few doormat qualities, although it's mostly because he's stuck being school teacher to local Villain Protagonist Vendetta. Having an evil red bird fiend constantly keeping him in check doesn't help much either.
Poison Ivy: If you had a middle name, it would be welcome!
However, she does have a spine, even though it takes some time to dig it out. The episode Harlequinade demonstrated that when angry enough, she's perfectly willing to blow the Joker away (with a machine gun!) with barely a second thought. Probably the only scene in the entire series where the two showed genuine mutual respect and affection, as fits to their twisted minds.
Stacy Rowe from Daria fits the bill, though she started to grow a spine in the final season.
Luxor the cat from Tutenstein, thanks to the magic that compels him to serve the pharaoh.
On King of the Hill, Bill can fit this trope sometimes, although it can be tragic just as much as it's played for laughs. He was really a go-getter guy when he was in high school and pretty tough and likeable, but his current doormat status is implied to partly be because he joined the army, but mostly due to his leeching, cheating, dominating ex-wife Lenore, who left him with a broken heart and a missing spine.
Bill: When people yell at me, I usually do what they say!
Bobby can be like this too, mainly because even for someone his age, he's astonishing easy to influence and can be pushed into behaving in strange ways just from being around certain people.
Cotton's second wife Didi is maybe the most extreme possible version of this. She's always shown as quiet, depressed, and submitted, all of which are desireable traits in a spouse to the Jerkass Cotton Hill. With little free will of her own, she seems more like a slave than a wife.
Lois' mother is also shown as being a doormat to her husband, essentially bending to his will and even suppressed her Jewish identity because her husband wanted to get into country clubs. However, when she discovers in another episode that her husband cheated on her, she firmly tells him to leave.
Lois herself is also an extreme doormat. While she does get angry at Peter's tendencies to embarrass her and other shenanigans he puts the family through, Lois always forgives him at the end of the episode and has never even thought about leaving him. She'll also rarely stand up for Peter whenever her father puts him down.
The Simpsons has Waylon Smithers, an assistant to Mr. Burns. For much of the series he helps with Burns' schemes almost unquestioningly, but he may be a subversion in that there are some schemes even he will object to at the risk of losing his job. (See "Who Shot Mr. Burns Part 1.")
Also from The Simpsons: As Homer became more of a Jerk Ass, Marge appeared to be more and more of a doormat, forgiving him over and over again, not only for stupid accidents and acts of ignorance, but huge acts of genuine deceit. While Bart and Lisa weren't willing to put up with it in many cases, Marge overlooked almost everything he did.
Finally addressed in the movie where Marge declares she had put up with Homer's jerkass nature and shenanigans long enough and decides to leave him. Homer spends the rest of the movie figuring out why Marge left him and what he can do to correct it.
Notable straight versions are Ned Flanders (specially post-Flanderization) and Kirk Van Houten.
A notable example is Seymour Skinner, obsessed with being the "perfect son" for his mother Agnes. Subverted in the Alternate Universe where he's actually Armin Tamzarian a rebellious orphan who took his Seymour Skinner persona from his mentor after Agnes mistook him when he was about to inform about the apparent death of the real Seymour in Viet Nam.
Sidekick: Golly Gee Kid the janitor, in his sidekick days, this is basically his job as Maxum Man's sidekick.
An episode revolves around her doormattitude, which has been turned Up to Eleven for the sake of the episode; she's even pushed around by Angel Bunny, who up until now tended to make it his job to keep everyone else's pushing around to a minimum. So she goes to a seminar on assertiveness, which causes a complete personality 180. She actually calls Pinkie Pie and Rarity worthless to their faces before the Heel Realization rolls around.
The Bushwoolies from My Little Pony were frequently troubled by the difficulty they had disagreeing with anyone, especially each other; their leader Hugster seemed to be the only one who really had a mind of his own. It was probably all they could do to decide to rebel in "Escape from Katrina" in the first place.
Pushover in The Smurfs episode "The Smurf Who Couldn't Say No", who basically is a Smurf who has trouble saying no until he accidentally causes the Marsh Monster to be released by extinguishing the ancient Foxfire Flame in the Great Swamp, and then he and Scaredy return to the swamp to relight the flame and Pushover insists on Scaredy doing the honors. By the time the episode ends, Pushover is no longer a pushover!
PJ on Goof Troop. Despite being the Only Sane Man, he is so insecure that he finds it difficult to say no to anyone, no matter how unreasonable their requests are. Max typically drags him into Zany Schemes despite his objections, while his father treats him like a slave on several occasions. Even his little sister pushes him around. He typically puts up a token resistance with Max (who always manages to break him without trouble), and no resistance at all with his father, mostly displaying his resentment while alone, though there are a few occasions he's pushed too far. He also takes verbal abuse and rejection without fighting back.
Mole from Mr. Bogus finds himself in this trope very frequently. It makes a lot of sense, since he often serves as Ratty's Sycophantic Servant and will very blithely listen to anything that he says.
Dan Vs.: Chris often gets roped into Dan's revenge schemes and eventually goes along with what he says while openly disagreeing with him. At one point, he has to remind Dan and Elise that he is his own person and can make his own decisions. That said, there are a couple of times where he puts his foot down like in "The Monster Under The Bed" or "Chris".
Most people have met someone like this. Often, these people either inspire the protective instincts of others or they're constantly taken advantage of. Many times, without meaning to, these people come off as somewhat creepy.
Corporate culture encourages this in some positions, such as cashiers.
Also, some cats, if you look at the page image.
This can be a sign of certain psychiatric issues. Often, people who have been abused, outcast, bullied, or in other ways mistreated can be very nice out of fear that if they say no, then bad things will happen.
The abuse survivor version of this is called Complex Post Traumatic Stress Disorder. It comes with a side of lack of self worth, inability to connect with others, and lack of ability to express emotions. It's particularly sad because to the sufferer, being treated like a doormat is better than being excluded entirely, and they're convinced that if they try to express and assert themselves again, then they'll just end up being hated.
Doug Walker has discussed this in early episode commentaries, where he admits to having no backbone and getting bullied for it, but it doesn't bother him because all he wants to do is be a Nice Guy.
Certain unhealthy friendships will have one person making absurd demands and the extreme lonely doormat folding to them, even at a personal cost and not feeling like they can pursue their own goals.