Sometimes, the type of hat a person wears can tell you a lot about their personality. However, these hats go a step beyond and noticeably alter the personality of their wearer.
The hat (or other headgear, like helmet or crown) may be a form of personality-altering Applied Phlebotinum. Particularly bad cases may function more like Demonic Possession, with the hat completely overwriting the wearer's personality. Or the hat may simply be a Magic Feather, giving the character the boost of self-confidence necessary to alter their behavior. However it works, the character's behavior is markedly different when they wear it.
A subtrope of Artifact Domination. If the hat alters the wearer's behavior for the worse, then it's also an example of Clothes Make the Maniac. If it's used by someone else to control the wearer it's also a Hypno Trinket. If the hat grants special powers to the wearer, it's a Hat of Power. It has very little relationship to Planet of Hats.
Compare Evil Mask.
- A bumper for Syfy had a woman try on a dress, only to be taken over by it.
- A more mundane example is Lance Temple's mask in Blaze of Glory, which if pulled over his face causes him to switch to his other personality, the Outlaw Kid.
- Doctor Fate's Helmet of Nabu would cause him to be possessed by the spirit of the deceased wizard, Nabu.
- The Serpent Crown in the Marvel Universe which grants the wearer various abilities. These abilities can include superhuman strength, the power to read and control the minds of others, the power to levitate oneself and other persons or objects, the ability to cast illusions, the power to project destructive bolts of mystical energy and even the mental ability to manipulate matter and energy. However, use of the crown usually leads the wearer to fall under the mental domination of Set, who then has the wearer perform various tasks which would help facilitate its physical return to the Earth dimension.
- Meet the Robinsons's Bowler Hat Guy could only dream of exacting revenge on his boyhood pal Lewis for ruining his chance at baseball stardom, until he was accosted by the robotic bowler hat DOR-15 "Doris", and he became the arch-villain of his dreams. Dream on, Goob.
- The Snowlems in "Cold Snap" are created by an ancient entity with no understanding of humanity, and were essentially without personality. However, her human acolyte gave them faces and hats and, in doing so, imbued them with a very basic personality based largely on the hat they wore. For example, the one wearing a top hat became the one in charge.
- In Wyrd Sisters, the crown of Lancre has absorbed the personalities of its past wearers, and when Granny tries it on out of curiosity she has a disturbing urge to start swanning around and chopping people's heads off. (The new king seems to be immune to the effect, though, judging by the sequels. Maybe you need to be magically sensitive, or maybe his personality's just so different that the crown has nothing to latch on to.)
- In Sourcery, the Archchancellor's Hat has absorbed power and personality from the Archchancellors of Unseen University who have worn it over the centuries. When it finds a wearer it likes, it's subsequently noted that it's more like that hat is wearing the man than the reverse.
- In Lords and Ladies, the meek Queen Magrat hides from the invaders in a disused armory where she finds the armor and helmet of the ancient warrior queen Ynci; she puts them on, and subsequently begins showing some of Ynci's character traits. This is a Magic Feather example, as it turns out in the end that the helmet and armor are fakes made for display in relatively recent times and Magrat is the first person to actually wear them in battle.
- According to Cohen in Interesting Times, the turban conventionally worn by the Grand Vizier. "Give 'em a turban with a point in the middle and it just erodes their moral wossname." This could just be a metaphor, though, as opposed to the Archchancellor's hat that literally has magical influence.
- In the second book of the Larklight trilogy, the mysterious hats are actually shapeshifting, mind-controlling, thought-eating aliens in disguise.
- The Svarog series by Alexander Bushkov mentions in passing an artifact called the "Black Crown". Presumably, it gives one great powers but burns their soul, making them instantly Chaotic Evil.
- Wax and Wayne: Wayne has several times stated that the correct hat is the key to a convincing impersonation, and during the few scenes we get from his POV he seems to take on the personality of whatever hat he's wearing (for example, in one scene he's wearing a policeman's helmet to infiltrate a station, and almost ends up thinking of himself as a policeman).
- There's a largely-forgotten Norman Wisdom sitcom from the 70s where his entire personality would change according to what hat he was wearing.
- Linda's magic hat from the Round the Twist episode "Copy Cat", which grants the wearer the power to fly but also starts changing the wearer's personality.
- In the original The Twilight Zone episode "Dead Man's Shoes", a homeless man finds the body of a gangster's victim, puts on his shoes, and is possessed by the victim. The '80s remake did a gender flip, "Dead Woman's Shoes", in which the trinket is a pair of shoes belonging to the murdered wife of a rich corporate type.
- Dungeons & Dragons
- Helm of Opposite Alignment. Instantly changes the wearer's Character Alignment to its opposite (e.g. Lawful Good to Chaotic Evil).
- The Crown of Souls will eventually change the wearer's alignment to Neutral Evil.
- The Forgotten Realms Horn of Crowns causes its wearer to act in a crazed and violent manner.
- Hat of Command: The wearer feels an overwhelming desire to take charge.
- Hat of Occupation: Wearer thinks and acts as if he's a member of another class, but isn't.
- Parodied in Munchkin with the Helm of Courage. It has no visor.
- In The Unexpectables it's revealed that the human warrior Luistrog was originally a grave robber named Jaret. The helmet he wears possesses whoever dons it and overwrites their mind. The new personality is continuous between bodies and is not really happy about their existence.
- The Helm of Dark Magics in Arcanum permanently raises your magical aptitude and lowers your alignment each time you put it on.
- The Peak Point helmets from Ape Escape. The most notable example is Specter, who goes from a cute and adorable monkey to a scheming, megolamaniac supergenius. The only exception to this is Pipotchi from 2, who wears a special pipo helmet designed by the Professor which increases his intelligence but keeps his lovable personality intact.
- In Bush Whacker 2 the Princess' hat makes her behave like a royal brat until she loses it at one point.
- While not shown when in Moga or Tanzia, the Shakalakas who accompany you in Monster Hunter Tri (Ultimate) change personalities depending on the mask they wear. Cha-Cha acts like a tough old man with the Ancient Mask, while Kayamba in the False Felyne behaves like a Lolcat.
- Mannick of Charby the Vampirate has a form of psychometry that allows him access to an individual's knowledge while affecting the way Mannick talks, thinks and behaves by wearing an article of their clothing they spend a lot of time in with a significant preference for hats. Some of these changes stay with him even after he has removed the item in question and there are hints he has access to the powers of said individuals while wearing their hats.
- In a EGS:NP storyline in El Goonish Shive, John Toutman gets a detective hat placed on his head, he claims wearing a detective hat does not actually help make him any more of a detective and yet he is immediately able to deduce where Susan ran off to when he wasn't able to before.
- Girl Genius
- When Agatha returns to Castle Heterodyne, the only way for humans to communicate with the castle's central brain is for the Seneschal to wear a helmet that inserts probes into his brain, allowing the Castle to take control of his body.
- In the "Trelawney Thorpe: Spark of the Realm" short story, the MacGuffin is the crown of King Arthur, which is supposed to give the wearer the power of King Arthur. What it actually does is give King Arthur the body of the wearer.
- In one Skin Horse comic, an avian-humanoid freaks out because Tip put on a hat. She believes that hats make you evil and instantly worthy of hate.
- In The Care Bears: Adventure in Wonderland, Grumpy Bear changed personalities every time he put on one of the Mad Hatter's hats.
- Darkwing Duck several times had to fight alien, sentient mind-controlling hats.
- The Looney Tunes cartoon "Bugs' Bonnets" has Bugs Bunny and Elmer Fudd switching personalities as various hats blow past and land on their heads.
- In one episode of The New Adventures of Superman cartoon, a possessed hat causes anyone who dons it to commit evil acts.
- Rocky and Bullwinkle has the Kirwood Derby, which makes its wearer the smartest person in the world.
- Ruby Gloom's Skull Boy has problems with this thanks to a "Shakespearean Love Hat." It causes him to speak proper Shakespearean when wearing it and also makes Iris & Misery fall for him.
- An episode of Sheriff Callie's Wild West centers around one character receiving a new wardrobe to turn him into a gentleman. Wearing the monocle transforms the wearer's voice and mannerisms to that of a high-class man, complete with the stereotypical Queen's English accent.
- Spliced: In "Follow Your Dreamworms", Entree snatches Joe's top hat and replaces it with a flowery sunhat. Joe's normally angry voice immediately becomes much more girly and singsong.
- In Total Drama: Revenge of the Island, Mike (who has multiple personality disorder) puts on a slouch hat and suddenly becomes an adventurer called Manitoba Smith.
- Doctor Fate's helmet (see Comic Book examples above) appears in Young Justice. It eventually ends up completely taking over the mind of Zatara.