Originally an ordinary salaryman, Saitama was inspired to become a hero when he managed to defeat a crab monster attacking his home town with nothing but his necktie. He trained for three years doing an ordinary if absurdly intense regimen of sit-ups, push-ups, and running until his powers awoke and he lost all of his hair. Now he's become so powerful that, no matter the opponent, he can defeat them with a single punch. Because of this, he's grown bored with his life of super-heroism.
Almighty Janitor: The strongest - but only class B. Not to mention that all of his observed victories are seen by the public as nothing more than flukes.
Anti-Hero: Definitely a Type Two. He has the power to completely change the world and is very very lazy. He's also quite cynical about the hero business. However, without a doubt, he will do the right thing.
Badass: So far, the strongest character in the series.
Badass Cape: Arguably the only thing he got right with his outfit.
Badass Normal: He managed to defeat a crab monster with nothing but his shirt tie before he ever even started training.
Bald of Awesome: In that his awesomeness is the reason he became bald in the first place.
Brick Joke: While talking with Genos before the training session, he wonders what his superhero name would be and comes to the conclusion that he would be called Caped Baldy. Several chapters later, and he does end up getting called Caped Baldy. He doesn't really like that.
Charles Atlas Superpower: Played with. His training regimen isn't even that intense; his commitment to doing it every day is noteworthy, but when he tells people about it they react with incredulity that it could have made him so strong. Genos even notes it would be impossible for a normal human being to reach Saitama's level just by training.
Comically Invincible Hero: Played with and explored - he almost had an existential crisis simply because he grew so strong he couldn't enjoy his hobbies anymore.
Dreaming of Things to Come: Played with and parodied. He has a dream about saving the world from the mole people who've risen from under the ground in order to wipe out humanity, and having a truly thrilling battle in the process. When he wakes up, the very same mole people from before are in the midst of launching their attack but, as usual, Saitama does not have a hard time at all defeating them.
Friend to All Children: He's shown giving a child lost in the mountains a ride home at one point, and his first heroic act was saving a child's life.
Groin Attack: Accidentally does this to Sonic at one point. Luckily for Sonic, he'd wanted to stop right before making contact instead of actually hitting him, otherwise Sonic would likely be nothing more than a red mess on a tree at this point.
Heterosexual Life-Partners: With Genos. He's not exactly thrilled by Genos following him around at first, but eventually warms up to him.
Humble Hero: He doesn't seem to care much about notoriety.
Jerk with a Heart of Gold: He became a super hero for rather selfish purposes, is lazy, and seems to care more about having a fun fight and will sometimes ignore problems in his city until he's directly involved, but he does genuinely want to protect the world. He's just fallen into a lull because of how easy it's become.
While he doesn't always act like a paragon of heroism, some of his lines imply that, while he may not act like it, his heart is in the right place. One of the best to date? "If the heroes run and hide, who will stand and fight?"
He's also quick to let people think he's a phony, just so that the other heroes who put their lives on the line and nearly died would get the respect they deserved. He doesn't care about getting recognition from the public, but thinks the weaker heroes should get it.
Logical Weakness: The drama of the comic comes from the fact that he can't fly. He can only walk, and gets lost a lot. Thus, whenever an Eldritch Abomination that he can kill in one hit comes along, he usually is the last to arrive to actually do anything about it.
Nigh Invulnerable: His training didn't just make him insanely strong, it also gifted him with incredible endurance, so much so that hitting him can actually harm his opponent.
The Nondescript: His baldness is the only strange thing about him, and even that just makes him look more like a cartoon stick figure.
"World of Cardboard" Speech: He makes one after some people say a lot of bad things about him, never mind that he saved them from a giant meteor in the first place.
Saitama: Let me make one thing clear! I'm not working as a hero to get you morons to admire me! I do it cause I want to!
Genos, "Demon Cyborg"
Genos was an ordinary boy until a rogue cyborg destroyed his home town and killed everyone he loved. He was mortally wounded, but a kind scientist saved his life and rebuilt his body. Genos traveled the world in the hopes of tracking down the cyborg responsible for killing his parents, but chooses to settle down with Saitama after a while in the hopes of also becoming more powerful. Whereas Saitama has raw, undeniable strength, Genos has everything else. That is, looks, intelligence, dedication, money, style, and appeal.
The Ace: Intelligent, cool-looking, and incredibly powerful. He even becomes one of the top 17 heroes right off the bat. It's just that Saitama blows him out of the water in terms of raw strength and invulnerability.
An Arm and a Leg: It's not a proper fight if Genos doesn't lose at least one limb.
Overshadowed by Awesome: Zigzagged as he, Saitama and a few others know who's stronger between the two, but most people think that he is the stronger one and assume that Saitama is using someone else's (possibly Genos's) fame, particularly in the entrance exam when the examiner thinks Saitama is nothing to write home about but sees Genos as being pretty impressive.
The Worf Barrage: We have yet to see any of his cybernetically enhanced strength or massive firepower actually accomplish anything on-screen. All of his victories tend to be beating the weaker minions off screen.
S Class Heroes
An unknown hero that has yet to appear in the original web comic.
Lampshade Hanging: The fact that nobody, not even the Hero Association, know much about him is repeatedly and mercilessly joked about - apparently, he's just shy, really fussy and has a thing about his privacy.
The Ghost: Has been mentioned by the characters, but has yet to appear.
An insanely powerful Esper. Has a younger sister, Blizzard, who is the 1st ranker of B-class heroes. She is generally abrasive and condescending to everyone she talks to, particularly lower-ranked heroes like Saitama.
Born Winner: This is basically the reason she's S-Class Hero Rank 2 - she was BORN with the level of power she has.
The Glorious War of Sisterly Rivalry: With Blizzard, who she thinks is wasting her time and talent in Class B and should ditch those losers and become the hero she was destined to be. Considering this is Tornado we're talking about, her saying her sister belongs in S-Rank with her might be a stealth compliment.
The Obi-Wan: Considered on taking Saitama and Genos as his disciples. They both decline, as expected. Genos probably did so due to how 'useless' Fang was in the face of overwhelming raw power. Saitama declines because he doesn't need to resort to martial arts when he has such an overwhelming stat advantage on every area and he probably wants to get a challenge.
He's also the former master of the now most powerful enemy in the series, "Hero-Slayer" Garou.
Secret Keeper: He's the only character besides Genos who knows about Saitama's real power.
4. Atomic Samurai
A swordsman who can cut you to nothingness, slicing your very atoms with a million slashes.
Cool Old Guy: Not that old, he is only 37... But don't tell him.
Just a Kid: Knows exactly how to use this to his advantage. Many a monster have been fooled into coming close to him, thinking him to be a harmless child... only to get a facefull of hi-tech guns and cutting blades.
Kid Sidekick: In his C-Class days. He was actually Metal Knight's lab assistant for a while.
A mysterious scientist controlling a powerful ballistic robot. He was sent along with Fang and Genos to destroy a meteor that threatened to annihilate Z-ville. His real name is Bofoy, but no one has ever seen him in person. He only appears in public with his remote-controlled robot that proves completely ineffectual to stopping the meteor.
His real name/"Civillian Identity" is Doctor Bofoy
For Science!: To get him to even appear to a fight, you have to promise him that he can take the monster/whatever back to his lab to study it.
Science Hero: He uses unmanned robot suits to battle monsters and builds Bunker-like buildings that are pretty damn resistent to being blown up for the Hero Association.
Villain Protagonist: We haven't even seen the man himself, but already Genos gets a warning about him from Enginite that he's not to be trusted.
The world's strongest human and the so-called most powerful hero of all times whose powers are said to be comparable to Tornado. The truth is, he's just a normal guy who happened to be in the wrong place at the wrong time. The rest of the cast never knows about King's true identity even when they're up against the most powerful enemy in the manga currently, all of them place their hopes on King.
Badass Arm-Fold: Is often seen doing this on the battlefield, standing aloof and alone, although that is because he doesn't know what to do with his arms and has to stop himself shaking because he can't fight.
Badass on Paper: Parodied. Even though he's powerless, King can still intimidate the enemies just by glaring on them, forcing them to flee in terror.
Born Lucky: Played for comedy - although he is rather pathetic, it still doesn't stop him from being S-Class through sheer co-incidences and sometimes absolute pure luck, simply because he's always in the right place, at the right time, and usually does something completely mundane that helps the situation.
Cowardly Lion: Although he confesses that he's always completely terrified of his opponents and considers himself a coward, he still manages to put up a strong front even against enemies that send other S-rank heroes fleeing, despite having no powers at all.
Fake Ultimate Hero: King just doesn't have the heart to tell people they're wrong about him because it might upset the civilians, and so the tales of his 'deeds' keep piling higher and higher....
I Owe You My Life: He got his scar from an Octopus-Claw Man and Mysterious Being that attacked one day, and if it wasn't for Saitama, he might have died then and there. It takes a while for him to recognize Saitama again, due to him not having his hair, but it's what cements the beginning of his friendship to Saitama
Foil: To Saitama; while Saitama is outrageously strong with no recognition, King is a totally ordinary guy who everyone thinks is an invulnerable superhero.
I'm Not Afraid Of You: Many monsters have tried this claim against King. He just continues staring at them, very intently. They don't keep their courage for very long after that. And King gets a moment to play this too, although he's scared of the amassed monsters of Society, he still is able to make them immediately be on-guard through using his reputation alone, is able to scare one of them out of his wits with a small comment about him watching his step and pratically scaring him into running for it (right into a regenerating Zombiman who was beneath the rubble), and ALL the monsters basically scattered when he unfolded his arms, right into the reinforcements.
Mistaken for Badass: He's the one who took all of Saitama's superhero deeds (from the very first chapter of Vaccineman) since he happened to be the only man in the vicinity.
Just to clarify to how badass his, or Saitama's true, reputation is: During the Alien invasion, all the heroes called to him to deal with the ship alone. When he declined due to the fact that he doesn't have any ranged attacks, Tornado calls him on it and wished to attack his reputation. Supershiny Black Allow pulls her back and tells her not to mess with King, or he'll kill her. When Genos tried to help her, but got threatened by Tornado and was about to retaliate, S.B.A says the same to Genos about Tornado's power.
Later in the story, Saitama gets to know his secret, and becomes his gaming buddy. King is VERY good at those games, to the point where the reputation he's earned in-manga actually applies to video games, such as absolutely broken infinite combos and being able to beat really hard games with one hand.
Outscare the Enemy: How King defeats his opponents, with a little help from "the King Engine", which is the DOOM DOOM DOOM sound he gives off which turns out to be King's own heart as he tries not to freak out
Poor Communication Kills: Played with - King doesn't get a word in on any sort of discussion most of the time, which leads to odd misunderstandings such as Child Emperor mistakenly thinking King can fire lazer beams. This gets the S-Rank heroes into serious trouble (until King draws attention to himself by pretending to do the move), which just makes his reputation reach even greater heights because "he used a special move to save all the S-Class heroes" is all that will get circulated in rumors later.
Snowball Lie: Played with - the lies are spread by other people, and almost every time that it seems like the bluff might get called, SOMETHING happens that is 1. Extremely lucky for King, because he no longer has to prove he can fight (most weak monsters have a small heart attack and collapse when he appears, and most strong monsters usually get engaged by another hero, which makes them think King was merely distracting them so the other hero could get the credit, Or Saitama one shots them completely coincidentally) and 2. Usually happens in a manner that somehow gives King all the credit for his incredibly lucky windfall (for example, piratically every kill Saitama does somehow gets accredited to King, no matter how absurd the logic jump is), so he gets a even bigger reputation for being the ultimate hero.
The Stoic: Played for laughs - see that really tough expression as his profile picture? That's the face he makes to stop himself from expressing absolute terror.
Victory Through Intimidation: King can turn the tide of a battle simply by showing up - his reputation alone makes monsters and heroes alike freeze in place, and villains that randomly run into him on the street literally have a stroke because he's that big of a surprise. And if you try to attack him? all you hear is DOOM DOOM DOOM DOOM DOOM, which can make even the most hard-hearted monster falter with doubt and reluctant to hit him, in case of it being fatal to themselves to even touch him. It's a good thing too, considering King has the fighting ability of a completely normal person.
An immortal superhero that simply cannot die. He will always regenerate no matter how bad his wounds are. He wields various weapons from chainsaws to axes to shotguns.
He's a product of the House of Evolution.
His codename at the House of Evolution was "Subject #66".
Dark Is Not Evil: Zombies are traditionally considered an undead monstrosity, not to mention that he comes from the House of Evolution. Despite all of that, Zombieman is one of the most heroic character in the series.
Establishing Character Moment: Introduced as he has finally found the trail of the scientist who created him (the House of Evolution antagonist), and having sworn to kill the scientist for his evil ways, talks with him (while pointing a gun at him) until the discussion shifts to how Saitama (his name isn't mentioned but the reader knows who the scientist is talking about) basically crushed his evil ambitions. Zombieman, seeing that the scientist has actually been "defeated" to the point he's dramatically changed, actually puts away his gun instead of shooting him.
Implacable Man: He WILL be back to kick your ass no matter how many times you knock him down. He will NEVER stop or surrender pursuing you if you're a threat.
Ludicrous Gibs: When he pulls out a sharp object, someone's gonna get chopped into pieces, and the battle turns into a messy bloodbath. Sure, most of the times all the limbs and blood scattered around are usually Zombieman's, but the difference is Zombieman's wounds heal and his limbs come back, and his opponents usually don't.
Terror Hero: Comes with being a zombie - the concept of a hero that just won't die until you are either under arrest, defeated, or dead, slowly but surely terrifies his enemies. Because absolutely nothing can kill this guy, nothing can get in his way, and he can hunt night and day to find and capture you. In fact, it's this sheer determination quality alone that got him to the S-Rank hero status in the first place, which makes him the only S-Rank Hero that got in due to his pure, absolutely unkillable defense instead of the absolute fighting strength that usual S-Rank Heros have.
Weak, but Skilled: He doesn't have freakish strength, or much offensive capacity at all, but his main skill is not being able to die, ever, and since he can practically regenerate from everything, with a skill like that you don't need to be terribly strong when you can simply outlast the strength of your enemy.
Why Won't You Die?: Gets this a lot from his enemies, mostly because no matter what, HE. DOESN'T. DIE. Blow his arms off? They come back. Blow his entire body to bits? They just regenerate together. Vaporize him to a atomic level? All that does is slow him down, because he'll have to regenerate from nothing and that takes longer.
A mysterious hero who doesn't appear much. He told Genos to "Be careful of Metal Knight".
Training Montage: Shown in-manga how he got his super shiny body - he lifted weights every day, going from a skinny scrawny guy who could barely lift into a superbuff weightlifter. There were two effects: His body became so muscly his muscles actually shined, and he became bald.
12. Watchdog Man
Superhero in a ridiculously funny dog suit. Able to rip apart his opponent with his claws.
Animal Motifs: In case you missed something, his motif is of a Dog - He took the term "city watchdog" literally, so he wears some sort of dog costume.
Beware the Silly Ones: He may occasionally speak in thought bubbles, but don't dare underestimate him, because he can rip through hundreds of monsters with ease. He's been slaughtering demon/dragon level monsters with his bare hands alone since his C-Class days.
Lethal Joke Character: When he says there's "nothing interesting to report", what he actually means is "Now that I'm here, I killed practically every monster in the area, and now there is no longer anything left to report to you".
Jerk with a Heart of Gold: Sure, he's quite arrogant (because he can move at the speed of light), but he compliments what he thinks is just a random B-Class hero (actually Saitama) on his noticeable muscles and gives advice to not forget about working on technique. He tells Saitama that he could even be an A-Class hero(which is a big deal for the average B-Class heroes) without any hint of sarcasm.
Jobber: Ironically, He's the only S-Rank hero that gets humiliated almost every time he appears. Tornado shows him up using her Psychic powers during the alien invasion and later Garou actually succeeds in beating him, signalling his confidence rise to taking on top A-rank Heros
A burly drag with gay yet super powerful special moves, loves good looking guys, addresses everyone with the suffix -chan
Arrested for Heroism: Played with - apparently he put HIMSELF into prison (with a infinite year sentance) because he didn't want to use his strength just to try and stalk guys. He literally breaks out of prision when given the call (he writes an apology note for the damage and promises to be back soon to make it okay).
Team Dad: When he teams up with the other S-Rank heroes, he's usually this to the point he uses his "fatherly instincts" to find the other heros when they all get trapped underground. He finds EVERY SINGLE S-RANK HERO this way, and he even gives moral support to them.
"The Reason You Suck" Speech: The Sea King really plays his attacks down and laughs at his conviction to protect men. Heck, during his fight with the Monster association, he even gets a small flashback of the insults Sea King threw at him... and then he shows offwhat he learned from that fight.
A Class Heroes
1. Handsomely Masked Sweet Mask
Anti-Hero: Genos says Sweet mask is basically what he could have been, if Saitama didn't enter his life. Consider at the beginning of the manga just how driven by revenge Genos was compared to how he is now.
Break the Haughty: Garou later appeared after Sweet Mask mocked the rest of the S class hero for failing to protect humanity, then proceeded to effortlessly defeat him, ending with caving in half of his face RIGHT INTO HIS SKULL, knocking quite a few teeth out.
He Who Fights Monsters: His face when he confronts the Monster Society warps and spasms in a nasty way, making him look down right freakishly terrifying, like he just took off the human mask he wore to let through the disfiguring anger and hatred for monsters he has inside. It's like he's letting it show through so he can have the determination to beat them.
Heroic Willpower: It's a ability he actually invokes - His arm gets sliced clean off... and he simply re-attaches his arm again and the arms still works. Remember, he's mostly a normal human, and not a cyborg like Genos.
Merchandise-Driven: Go ahead, give him even a small amount of room to promote some of his merchandise. He'll talk about it anyway whether or not you prompted him.
Weaksauce Weakness: He just can't deal with really ugly looking people. This comes back to bite him later when he encounters a Ugly Mysterious Being, and his body pratically freezes stiff from looking at it.
Badass : Pretty much one, considering he is Atomic Samurai's best disciple and Rank 2 among A-class heroes. He also survived A-city's nuking.
Meaningful Name : His name is based on "iai" and "aian" (iron), referring both to his swordsmanship and his armored appearance.
Badass Normal: While he does take a lot of damage in the process, he single-handedly took out nearly all of the Sea King's underlings on his own. Each of them was, individually, ranked a Tiger level disaster. The main reason he took any damage? Because he was worried that his ultimate attack would hurt the innocent bystanders cheering him on. Given that it one-shot four opponents in one go, he was probably right.
The Don: Sort of - Class B has become an almost Mafia-like system due to all the strong Class Bs being loyal to her, and basically forcing the other heroes into working in Class B for the rest of their career since she kept the number 1 spot.
The Glorious War of Sisterly Rivalry: With her power, she was meant for great things and would've been the number 1 of many things in life. Sadly, her sister came first, and being a super-powerful Esper in her own right, she completely eclipsed her in everything. This causes a little friction in that Blizzard firmly believes the power has gone to her sister's head and made her the aloof, alone jerk she is today.
Meaningful Name: In one of the flashbacks, someone calls her "president Fubuki" (Fubuki means "Blizzard"), implying that just like her sister's, her Hero name is also derived from her actual real name.
Weak, but Skilled: Her Esper Powers count as this, as she manages to defeat a friend from her past, who turned into a mysterious being, that just minutes ago decimated her stronger, S-rank sister by using a new technique. The technique is sort of like a psychic shield that used tons of weaker psychic waves that turn to divert the far more powerful psychic straight waves from opponent's attacks. In other words, think of it like a tornado of psychic energy with Blizzard as the eye of the storm, and anything entering the tornado gets its energy stripped right off it due to the clockwise/counterclockwise swirling "wind".
Authority Equals Asskicking: Subverted for the most part, but as far as C-Class strength heroes go he's this, and that's mostly because he stops EVERY crime he sees while on patrol. All of them. Yet, he failed to save any person in the series (Mostly what happens is the antagonistic thing of the weak simply concentrates on beating up Licenseless Rider while the original victim escapes). Nonetheless, his heroic resolve is quite amazing.
By-the-Book Cop: So much so that He even stops Tanktop Master, a S-Rank hero, from beating the life out of Garou (by jumping into his attack, no less!) because it would be murder if he killed a street punk like that without giving him a chance to better or surrender himself peacefully. Of cource, Garou returns the favour by smashing his head into the concrete, but hey, you gotta give License-less Rider props for his unwaivering determination to do things legally.
Hero Stole My Bike: Played with - Having a bike is his gimmick, and everytime he gets trashed his bike usually gets bent horribly out of shape along with him, so he's given a new one.
Heroic Resolve: Actually goes up against the Sea King, knowing full well he's not strong enough to stop it, and delays it long enough for Saitama to show up and do his thing. Hell, Saitama even compliments him on it and tells him that in his eyes, he'll always be a true hero, no matter what rank he is.
Running Gag: Throughout the manga he appears at the scene, only to get quickly taken out off panel. This gets subverted in the Sea King arc
Too Long; Didn't Dub: The Viz translation kept his name as "Mumen Rider", even though "License-less Rider" would have been a perfectly acceptable translation.
An organization founded by Dr. Genus to pursue the goal of human perfection though artificial evolution. First antagonist fought by Saitama and Genos and easily anhilihited by the master and his disciple. After being defeated by Saitama, House of Evolution becomes a takoyaki stand.
Victory Is Boring: The entire reason he became a galactic conqueror was in the hopes that one day, he'd find a enemy worth fighting.
"Hero killer" Garou
Arrogant Kung-Fu Guy: Used to be Bang's top student, before Bang found out Garou wanted to be a Monster. Garou is still quite confident of his skills, and pushes his limits daily which backfires because Bang gets worried Garou might become a unstoppable monster that he calls his brother, Bomb, for backup, and together they kick Garou's ass straight to the monster hospital. Yes, the monsters have a infirmary for monsters that get beat up by heroes and survive.
A Twinkle in the Sky: Eventually Saitama uppercuts him so hard he flies into orbit... AND THAT STILL DOESN'T KILL HIM, it just makes him dissapointed that Saitama's strength is unfair, so he just resolves to become a "unfair Evil" in order to stand against him and he comes in a bigger form.
Berserk Button: Absolutly DO NOT be a condesending jerk about Justice and Heroism in Garou's prescence unless you want the most humiliating beatdown of your life, which Sweet Mask learned the hard way when he tried to give a lecture on how pathetic the S-Ranks were being mid-battle. Garou responds by literally punching his face in, mid-rant.
Card-Carrying Villain: He has "Hero Killer" as a title, He introduces himself by walking into a meeting in the Hero Association, One that is full of various rouges and evil doers (in-context: The association was putting the word out about the world-ending prediction, hoping the Underworld might decide the world ending is against their own self-interests), and loudly proclaiming they are all weaklings and that he, the Human Monster, could defeat all of them right here to prove it.... and then he actually does it. And then he goes for a casual stroll while making a threat at the Hero Association head.He also doesn't pay for his meals.
Came Back Strong: One of his abilities is "What doesn't kill me, only makes me stronger". And he's become very, very strong indeed.
Curb-Stomp Battle: Both played seriously and played for laughs - played seriously in that Garou is really brutal in beating up heroes, then played for laughs when Saitama lightly "tap" punches him for Dine-and-Dashing, which is results in a OHKO But immediately goes back to serious because Garou SURVIVES THE PUNCH. This means that his special abilities pretty much make it so that he adapted to Saitama's insane strength, which basically makes him unbeatably strong, and it puts him on the fastlane to becoming the Mysterious Being DemiGarou.
Then brutally subverted. Even when he evolves over 4 times, Saitama is still beating him so brutally that crushed his "unfair evil" ultimate mode, regressing him to his original form and leaving him barely standing. Saitama is not even scratched.
Even Evil Has Standards: Isn't interested in killing civillians like "some sort of crazed mass murderer" - He's only a Monster to fight Heroes - And still takes time help some fat kid with his bully problems who is later kidnapped to lure out said Heroes by the monsters, repeatedly, But the latter times were mostly to save the kids life from Garou's monster allies who would have killed the child. Yes, Garou kidnaps the child back from the other monsters, just so a hero is guarenteed to come after him.
Foil: To Saitama; their backstories are extremely similar, save that Garou wanted to be a villain rather than a hero.
Good All Along: Saitama certainly thinks so. He (and the other Monsters) notes that Garou went out of his way to avoid actually killing any humans during his so-called Hero Hunt. He also reveals that Garou's threat to kill the child he spent his entire story arc protecting was a bluff by pointing that Garou was walking in the wrong direction. Saitama quickly grows bored of their fight for this very reason: Saitama became a Hero because he wanted to fight villains. Garou isn't a true villain — he's just a guy making a ruckus in Saitama's neighborhood.
Good Thing You Can Heal: Another of his abilities, the ability to adapt his body and slowly heal himself. His body is physically battered - his ribs have been broken A LOT, and that's not accounting for all the other damages he's accumilated over the years.
Horny Devils: His appearance plays with it. His horns used to be his hair before hhe gained the desire to become a real monster for heros to fight. This does two things: it changed his physical appearance to that similar to demon, and all his hair turns into his two "horns", leaving him bald.
Hero Killer: Oh come on, it's in his villain nickname. Near the end of his arc, He beats nearly every single hero that was S class, which includes Tornado, and even the A class number 1 without any effort. Though Saitama notes that Garou didn't actually kill any of them.
Knight of Cerebus: Ultimately, this is the sort of Monster Garou wants to become - the type of monster that, once it appears, changes the atmosphere of a battle completely. He actually succeeds, too - he becomes capable of defeating almost all the S-Rank heroes and he actually makes Saitama fight seriously-ish, and survives several of his serious punches, to the point of large area destruction, even when he didn't managed to even hurt Saitama in the end and he got bored of the fight.
Mook Horror Show: probably the best example, since he managed to last an entire fight against Saitama. Not only he is a category above the entire S-class heroes, but his abilities went to the point that he could block literally light-speed punches, and cuts that could split atoms, by evolving god-like abilities in martial arts. Then Saitama, an amateur with "normal punches", crushed him over and over again, to the point that he crossed all the possible ways to defeat him.Due to this, Garou labels him the representation of the unfairness of justice. Even becoming the unfairness of evil left him only as a punching bag for a couple of minutes.
Power Makes Your Hair Grow: His hair grows outwards wildly, and becomes more horn-ish as he fights and becomes stronger until he transforms into a mysterious being and his hair becomes real horns. He goes bald in exchange, though.
Sole Survivor: He is the only villain so far that has had a fairly serious battle with Saitama and is still alive.
The Faceless: As Demi Garou - although you see a few features, eventually he gets so strong due to Saitama getting serious on him, almost everything about him is blacked out and featureless - you can't even tell WHAT he looks like anymore. And then Saitama literally punches his face off.
Wild Card: Garou doesn't have any qualms about massacring weak "villains" or monsters that disappoint him. He also has a weird habit of letting the Heroes he savagely beats up live, simply so they can get stronger for the eventual rematch.
The Worf Barrage: In the end, his self-evolution-adaptability powers. Each hit of Saitama literally made him stronger and stronger until he became a demon-god like being.... and then it simply couldn't go higher, and ended up regressing him with each subsequent punch ultimately reverting him to his human form. Saitama literally killed his ultimate villain concept of Came Back Strong, one attack at the time.
Would Hurt a Child: Garou taunts the defeated S-class heroes by threatening to kill the boy who has been used as a hostage throughout the story arc. Saitama calls his bluff, pointing out that Garou was walking away from the boy instead of towards him (Saitama was the only person whose night vision was good enough to see this).
The One Punch Man setting has a lot of monsters and mysterious beings, mostly due to a currently unknown factor (although some beings have a explained background). In usual circumstances, these monsters would be quite dangerous, but in One Punch Man these creatures usually exsist simply to be reduced to a fine red mist in a single panel the moment Our hero, Saitama, shows up. There are some subversions to this, like monsters that are fought by other heroes being shown to be quite strong, and the monsters are slowly getting tougher, and they even have their own secret society, so expect longer articles the further into the series we go
Amusing Injuries: The first time he fights Saitama, he's defeated via a Groin Attack. In their second fight Saitama smashes his face into the ground so hard that in the extra page it's shown that it left an imprint on the concrete.
Beware the Silly Ones: This could apply to any villain that Saitama defeats, but this especially goes for Sonic. While mocked for his redundant name and being curbstomped by Saitama in very humiliating ways, it should be noted that Sonic's anything but harmless — He was effortlessly killing the Hammerhead group before Saitama showed up, and in their fight in Z-City he took out Tanktop Tiger in one shot and was leveling houses and buildings with ease.
Blood Knight: He's positively thrilled when he comes across an opponent who can actually be a challenge.
Card-Carrying Villain: Declares himself as one during his second encounter with Saitama in order to goad the latter into fighting him. This works much better than expected, as Saitama was in the middle of searching for a villain to defeat in order to prevent him from losing his hero status due to inactivity.
Time to Unlock More True Potential: You've got to hand it to him, he trains really hard to try and give Saitama a challenge. Not that it helps, mind, but still he goes off to train and get more abilities after almost every defeat.
Unknown Rival: Although he declares himself to be Saitama's rival, the difference in strength is obvious and Saitama even has a difficult time remembering his name (he calls him "Cross of Bones Panic").
Bang's only disciple. Quite the braggart.
Berserk Button: Pressed each time someone lacks respect (for him at least) to his master.
Small Name, Big Ego: He thought he could take Genos and Saitama to a fight. Genos proved him otherwise.