Darryl Walker (Damon Wayans) is a clumsy nerdy repairman, who is a genius and Batman fan. Darryl has a pure heart and an optimistic Pollyannish personality. He is childishly naive to the realities of living in an inner city neighborhood. The area suffers from political corruption and the police are on strike. It takes the murder of his grandmother, an avid supporter of Alderman Marvin Harris' anti corruption campaign for Mayor, by members of mobster Michael Minelli's gang, to awaken him to the realities of his city's urban decay.
He expresses his frustrations by intervening in a situation and boldly saving an elderly transit passenger from being mugged, and by ranting about the general corruptible state that the city has become. Darryl was so pure and shielded from reality presumably because of his interest in inventing, that he does not even realize that there is a "crackhouse in front of [their] flat". He tries to storm into it unarmed and rebuke the gang members, oblivious to the hazardous stupidity of doing so.
Awakened to the city's issues, Darryl is inspired to become a vigilante super hero. He uses his technical expertise to create weapons and gadgets. His brother Kevin, a tabloid news cameraman, goes along with this fantasy, believing that it's Darryl's way to cope with the murder of his grandmother. Darryl demands an audience with the police commissioner, but the police are not impressed with his actions, ridicule him, and arrest him for disturbing the peace. Darryl is released on orders to see a psychiatrist.
The psychiatrist calls Darryl normal, but a geek, infuriating Kevin, who the psychiatrist then attempts to psychoanalyze. After Darryl is nearly killed trying to protect a citizen on the street, Kevin tries to get him to tone his activities down, advising him to start a neighborhood watch. After he delivers a woman's baby in an elevator, he is asked for his name. Darryl just stares, and Kevin replies, "He's gone blank, ma'am." Both the lady and the reporters interpret this as a name: Blankman.
Over time he protects various other people in the community, building up a reputation and inspiring both the town and other real life superheroes. Kevin, hoping to win the affections of Kimberly Jonz, a reporter at his TV station, begs Darryl to allow her to interview him. He relents, on the condition that she wear a carnation. He brings her to his secret hideout, an abandoned subway station, and they talk about how he took up his duties to memorialize his grandmother and prevent crime. Impressed by his heroics and modesty, Kimberly immediately falls in love with Darryl and she kisses him causing him to have an erection.
Mayor Harris, who refused Minelli's attempts at bribery, attempts to bring in outside money to pay the IOUs the city has been giving its workers. He also requests that Blankman be there to protect the people and receive a special award. As the money is released, Minelli's henchmen storm the bank and take the mayor hostage, threatening to detonate explosives. At the police chief's request and the crowd's chants, Blankman attempts to save the mayor but is unable to defuse all the bombs.
He reveals his identity to the mayor and tells him of his grandmother's support for the mayor. Mayor Harris wishes him well, warning him to run and says he will tell Mrs. Walker about Darryl. Blankman runs out screaming as the bank explodes, killing Harris. The crowd, seeing his failure, turn on him, chasing him down the street. Darryl then gives up his heroic works for a normal life, getting a job at a McDonald's.
Wanting a great story Kevin's boss Larry Stone, a tabloid news junkie, manages to contact Minelli and trades knowledge of Blankman's love for Kimberly in exchange for an exclusive interview. In the midst of doing research on Minelli and Darryl's grandmother's death, Kimberly calls Kevin with the news. As Kevin answers, Minelli takes Kimberly hostage. Minelli issues a verbal threat to Kevin (thinking he is talking to Blankman), telling him he will kill Kimberly if Blankman does not show up.
Kevin rushes to Darryl's workplace with the news, but Darryl refuses to help wanting a normal life. Kevin finally convinces him with the news that Minelli had their grandmother killed and that he will wear the costume Darryl designed for him. The two rush to Darryl's underground lair where he again turns into Blankman. Kevin becomes his new sidekick but without a name. He just goes by "Other Guy". The two heroes then rush to the TV station.
After shooting the reporter interviewing him, Minelli becomes fed up. While threatening Stone, Blankman and Other Guy crash through the window and attempt a rescue. The two engage in a fight with Minelli's goons, losing. They are placed in a water tank and left to slowly drown. Stone and Kimberly are chained to desks and left to die as Minelli has hidden bombs in the building. At this point, Blankman calls in J-5, his robot assistant, to save them. J-5 drills a hole in the tank and the pair kick their way to freedom at the last minute.
The duo then search for the bombs, finding them in a women's bathroom. Activating J-5's "bomb disposal mode," Blankman stuffs the explosives inside and frees Kimberly. Stone is left behind, a joke Other Guy wants to play on his boss. Once outside, the explosives detonate, destroying J-5. Distraught, Blankman swears revenge.
Tracking Minelli to his hideout in a factory, the two prepare for the final battle. Other Guy, however, is overconfident and is wounded because his costume is not bulletproof like Darryl's. Blankman then defeats Minelli's goons with his electric "newchucks" (nunchucks). Just when Minelli is about to kill Other Guy, Blankman activates his jet-powered roller blades and captures Minelli and delivers him to the police. Blankman is once again acknowledged as a hero (this time, along with Other Guy) by the people, receiving the Mayor Harris Award for outstanding community service at a ceremony in their honor. Other Guy receives a Blankman t-shirt (much to Kevin's disgust).
After the ceremony, Kevin introduces Kimberly to "Darryl." The two make light conversation until Kimberly pretends to see a purse snatcher, putting Darryl on alert. Kimberly then reveals she knows that they are Blankman and Other Guy, and she kisses Darryl to prove it.
Darryl falls to the ground after getting the same embarrassing reaction he had the first time while Kevin and Kimberly laugh at him. The film ends with a shot of a banner that reads "We Love You Blankman...and the Other Guy".Damon Wayans as Blankman/Darryl Walker. A nerdy and gullible manchild who decides to become a superhero in order to turn his neighborhood around. His best friend is a homemade robot he calls "J-5".
Michael Wayans as Young Darryl
David Alan Grier as Other Guy/Kevin Walker. Darryl's cynical older brother who works as a cameraman for the local news. He initially had no interest in being a superhero but he later has a change of heart and joins Darryl as his sidekick.
Damon Wayans Jr. as Young Kevin
Jon Polito as Michael "The Suit" Minelli. A suave yet malicious and mean-spirited mobster who constantly harasses Mayor Harris. He is also responsible for the death of Grandma Walker after she insults him.
Robin Givens as Kimberly Jonz, a TV news anchor, and the love interest of both Darryl and Kevin. While she has no interest in Kevin, she falls in love with Blankman/Darryl almost instantly and harbors a strong sexual desire for him.
Jason Alexander as Mr. Larry Stone, Kimberly and Kevin's perverted, hot-headed boss. He is wheelchair bound, and is very selfish.
Lynne Thigpen as Grandma Eleanor Walker, Darryl and Kevin's late grandmother who was murdered by Minelli's assassin for an earlier insult. Despite being a loving grandmother, she has a smartmouth which ultimately led to her doom.
Christopher Lawford as Mayor Marvin Harris, The city mayor
Nick Corello as Sammy the Blade, Minelli's right-hand man, and assassin. He is the one who killed Grandma Walker.
Harris Peet as Commissioner Gains
Arsenio Hall as himself
Tony Cox as Midget Man
Blankman received negative reviews from critics. The film was not successful at the box office, but eventually became a cult favorite, with airings on TV and movie rentals.