Not Always Nice

Not Always Nice is the opposite of both Beware the Nice Ones and Not All Bad. In a lot of stories, the villain/villainess is quite presented as a Nice One to the heroes/heroines. But at some moment, they reveal his/her true nature by betraying the protagonists and revealing his/her negative intentions. The evildoer can even prove to the audience in the story that looks can truly be deceiving. Any villain, who acted as nice one, have ways to gain trust in the hero/heroine for their own purposes.

Sometimes it may happen that the hero can become a villain.

There are a few reasons these people may act like this:
 * They may want to be selfish and arrogant or just unbiased to either side, but their morality keeps on getting in the way, even if it is to their detriment. They may put on a rude façade to try to counter it.
 * They do consider themselves as better than everyone else, and their attitudes range from highly smug to insufferably intelligent to hubristic. After all, it is difficult for them to be nice to people when they do not even respect them. However, they still feel compelled to help these lower creatures on a regular basis.
 * They are natural loners. Their senses of duty force them to perform heroic acts, but they do not consider chitchat or politeness to be parts of their obligations.
 * They may want to be affable people, but they believe that being nice does not always get things done, and that accomplishing good requires them to do harsh and cruel acts, particularly if they have to teach something. (This may be an intermittent effect, applied only when necessary; contrast "Beware the Nice One"s, where such outbursts result from break-down. On the other hand, emotional trauma can coincide with the realization that nicety won't cut it.)
 * They cannot afford to let others get close to them because their enemies will use others against them.
 * They might wish to be nice but live so far outside normal human experience that they have no idea how to go about it; similarly, the hero might be autistic, or a non-human alien.
 * The world the heroes live in is operated through cynical ends, so the "strict good guy" routine does not work - either in the eyes of the author or in a literal in-universe sense.
 * They intimidate enemies through harsh demeanors.

Movies

 * Disney/Pixar
 * Lots-O'-Huggin' Bear: Initially acted like what his name implied towards Woody and the gang, but later reveals his true twistedly evil nature.
 * Stinky Pete: Initially was friendly towards Woody, but later reveals his true mean nature as he framed Jessie for turning the television on and is determined to go to the Tokyo museum with the whole Roundup Gang, regardless whether the others want to go or not.
 * Prince Hans: for most time was nice and charming to Anna, but later reveals that he never loved her, he was just manipulating her to take the throne. He then locks her in the room to freeze.
 * Henry J. Waternoose: Initially was friendly to Sulley most of the time, but later reveals his dark nature to Sulley and Mike after being convinced by Randall to assist him and learning about Boo as he saw her as a threat to his business. Afterwards, Sulley tries to reason with Mr. Waternoose and make him change his ways by telling him things do not need to be the way they are, only for Mr. Waternoose to tell him that he has no choice since scaring is no longer efficient.
 * Thunderclap: Initially was nice to Arlo, but quickly reveals his true carnivorous nature by devouring the critter.
 * Clayton: Initially posed himself to be a kind (if somewhat impatient) guide to Tarzan, Jane, and Professor Porter, but later reveals to Tarzan while locking him up that he planned to cage all the apes from the very beginning and sadistically praises Tarzan that he owes it all to him.
 * Charles Muntz: Initially was nice to Carl and Russell, but then reveals his true nature with the intent to capture Kevin as his search for Kevin's species made him bitter.
 * Lyle Tiberius Rourke: was initially nice and friendly to Milo Thatch for most time, but later reveals his true nature with intent to get the Heart of Atlantis.
 * Robert Callaghan: Initially was very friendly towards Hiro Hamada and his friends. However, after a lab accident ends with his daughter Abigail disappearing that Hiro and his friends near the climax of the film discovered, Callaghan, survives the fire that killed Tadashi with Hiro's Microbots. Later, Callaghan becomes known as the supervillain Yokai, seeking revenge on Alistair Krei, whom he blames for the accident.
 * Dawn Bellwether: At the start of Zootopia, Bellwether appeared harmless and seemed to be kind to Judy Hopps, understanding how she felt and convincing Chief Bogo to let her off the hook. In the final climax, she revealed herself as the mastermind behind the savage attacks in Zootopia, darting predators with a serum made from Night Howlers so prey animals can rule the city.
 * Ernesto de la Cruz: was initially nice and friendly to Miguel sharing with him passion and interest in music, but later he reveals his true nature to Miguel after admitting his murder of Hector.
 * Evelyn Deavor: Like Cassie, she started out as a friendly, loyal, and kind-hearted lady who is eager to help others. She is also laid-back at times. Unfortunately, she later reveals her true nature when she unmasks herself as the real Screenslaver. During the confrontation, she revealed that she never supported her brother's mission in bringing supers back into public and plans on keeping them illegal forever.
 * Stromboli: Initially was at first nice to Pinocchio, but quickly reveals his true nature as a greedy man by locking him in a cage and intending to later destroy Pinocchio in fire after he is no longer useful.
 * Edgar Balthazar: Initially was very loyal and friendly to Madame Bon Famile but after hearing that her cats get her fortune, he decides to get rid of them so he can have the fortune for himself.
 * Anakin Skywalker : at first he was a Jedi Knight fighting on the Light side of the force, but by Emperor Paplatine joned to Dark Side of the Force and he become Dark Lord of Sith named Darth Vader.
 * Will Teasle: first appearing as a well respected and kind sheriff, Teasle eventually shows his true nature when he arrests John Rambo for no vagrancy (even though he was innocent) and lets his deputies abuse him to his breaking point which nearly leads to the destruction of the town.
 * Sloan and Bree Blackburn: Initially posed themselves toward Eliza Thornberry to be friendly, warm and kind-hearted couple of animal-loving zoologists, before later revealing themselves to actually be the ruthless poachers who kidnapped the cheetah cub Eliza tried to save, and also plan to kill a herd of elephants with an electric fence.
 * Obadiah Stane (Marvel Cinematic Universe): Initially was at first nice to Tony Stark, but later reveals his true nature where he actually wanted to always in control over Stark Industries.
 * Happy Chapman: While this TV pet show host may look like he lives up to his name, in reality, he is an arrogant, selfish, and greedy jerk who abuses his assistant Wendell, and is not satisfied with his job as a TV pet show host. His original star pupil was a famous cat named Persnikkity, whom he grew tired of due to his allergies and then puts Persnikkity in the city pound. Chapman wants a dog to star in his show so he can overshadow his more successful news anchor brother Walter in fame. So he steals Odie for his own gain and then uses a dreaded shock collar on him, and even laughs at the dog's pain from the powerful jolts.
 * Darla Dimple: Initially appears as a sweet little girl who loves animals, but reveals herself to be a complete egomaniacal, psychopath, and rotten to the core spoiled brat who wants the spotlight to herself and is afraid Danny and his animal gang will ruin it and is determined to stop them at all costs.
 * Moo Nieu: Briefly appears as an innocent cow who is eating grass, but reveals himself as Betty's protector when he notices the Chosen One.
 * Boingo: For the most part, acts like the cute little bunny he appears to be towards Red, Granny, Wolf, Kirk, and Twitchy, but later reveals himself to actually be the evil Goody Bandit (however, Wolf and Twitchy already were skeptical about Boingo).
 * Tobias Beckett: Like Boingo, he acts like a friendly, wise and helpful mentor to be towards Han Solo, but later reveals himself to actually be greedy, egotistical and manipulative cheater who was tries to profit from unsold Coaxium and transport it to many different gangs.
 * Cecil Fredericks, Gus and Reginald: These elderly security guards at the American Museum of Natural History. Initially acted kind towards Larry Daley, but later reveal themselves to be after the stealing the tablet of Amuk Munrah and other valuable objects, wishing to retain their health and fund their retirements, the three plan to frame Larry for the real thefts and disabled the tablet to stop the exhibits from interfering.
 * Eric Knox: Tricked Charlie's Angels into believing he was an innocent, but then revealed his true colors and plotted to kill Charlie.
 * Jack Torrance: Initially appears as a loving father to Wendy and Danny, but later becomes a psychotic killer after descending into madness at the Overlook Hotel.
 * Sebastian Caine: Initially appears as a normal person, but later becomes a killer after lying to the government and testing the invisibility serum on himself.
 * Miranda Frost: Briefly appears as an agent assigned to work with James Bond by M, but later reveals that she is the one who betrayed James Bond and that she is working for Gustav Graves.
 * Emperor Palpatine: Initially starts out friendly, kind and humble, but during the climax of Revenge of the Sith, he is revealed to be Darth Sidious.

Cartoons

 * Eddy's Brother: At first seemed to be a loved brother to Eddy, but quickly reveals his true sadistic nature by mercilessly abusing his brother.
 * Tord: At first, he was friendly towards Edd, Matt, and Tom, but later revealed his true nature by showing his dark side and later revealed his robot, so that he can cause terrorism towards someone and their house, which he also planned to destroy Edd, Matt and Tom, and their house.
 * Starlight Glimmer: Initially was nice to Mane 6, but later reveals her true malevolent nature by stealing their cutie marks.
 * Gabriel Agreste: The fashion designer, he is actually Hawk Moth.
 * Tangier: Initially was friendly to Russell Ferguson, but reveals his true nasty nature by putting hot sauce at Russell's food.
 * Miss Mirimoto: Appeared as the noble teacher of the martial arts academy, but revealed her evil nature when she used Miyumi and the Mystery, Inc. Gang in her plot to bring down the modern realm so the ancient ways can thrive.
 * Josh: In the Rugrats episode titled "The New Kid In Town," he seemed like a friendly boy to Tommy, Chuckie, Phil and Lil, but later turns out to be a demanding and belligerent bully.
 * Vicky: Appears as a nice and kind girl and ally to Mr. and Mrs. Turner, but quickly shows her true nature when she tortures Timmy Turner.
 * Lil Gideon: Appears to be nice and cute to everyone in Gravity Falls, posing as a psychic, but later he reveals his true nature to Dipper when he tricks him to come to his family's factory and tries to kill Dipper.
 * Ted Dymer: In the Batman: The Animated Series episode "Beware the Gray Ghost", he starts out as a normal toy store owner when Simon Trent is selling all of his Gray Ghost collection, but later reveals his true nature when Batman and the Gray Ghost discover that Ted is the Mad Bomber.
 * Bismuth: she was very friendly to Steven and Crystal Gems, but shw her true dark nature to Steven Universe about utilizing the Breaking Point to shatter the Gemstones of Homeworld Gems.
 * Varian: Initially a nice, friendly, and helpful ally to Princess Rapunzel and her friends, but later reveals his true vengeance-seeking colors to Rapunzel betraying her.
 * Harumi (Ninjago): Princess of Ninjago, but later reveals she is the leader of the Sons of Garmadon.

Others

 * Arthas Menethil: Started out as noble, honorable and righteous knight of the Silver Hand, and the prince of Lordaeron, but after taking up the cursed runeblade Frostmourne, he became a malevolent, cold and ruthless death knight, led the Scourge in destroying Lordaeron, and merged with the Lich King.
 * Harvey Dent/Two Face: Started out as loyal and honest ally and friend of Batman, but unfortunate accident, make that become a criminal as Two-Face
 * Cyrus: Appeared nice and helpful to Ash, Dawn, Brock, Cynthia, and Officer Jenny at first, but later revealed his true nature when he revealed himself as the leader of Team Galactic.
 * Cassie Rose/The White Pumpkin: was initially friendly and harmless to Jesse's gang and the Youtubers for most time, but later reveals that she is The White Pumpkin.
 * Charlotte Pudding: she appeared with a sweet personality, it is revealed that it was all just an act and she is conspiring with her mother to eliminate the Vinsmoke Family.