Psycho Mantis was born in a small Russian village before the collapse of the USSR. His mother died giving birth to him, which made his father resent him. He discovered his father's true emotions while accidentally reading his mind. He wondered if his father would kill him, and the shock of this revelation awoke his subconscious. He used his telekinetic powers to burn down the village that he lived in, killing all residents. This release of psychic energy caused severe burns across his body, particularly his face.
The official cause of death for the people of the village was found to be brain hemorrhaging and he was then taken into custody by the KGB, which found his psychic powers impressive. He was taught to hone his abilities in a boarding school owned by Soviet Intelligence, along with other possibly psychic children.
After the collapse of the Soviet Union, Mantis was drafted as a psychic investigator by the FBI. He moved to the United States and began to work immediately for the FBI. He would enter the minds of suspected killers and uncover the truth about their crimes. However, while interrogating a certain serial killer, he dove too deeply into his mind. As a result, he adopted the personality of this serial killer and became psychotic. He eventually left the FBI and became a freelance psychic, offering his services to the highest bidder, and was eventually enlisted into FOXHOUND. By this time he had taken to wearing a gas mask, partially to hide his deformed facial features, but also to prevent the thoughts of others from entering his mind.
Metal Gear Solid 1
Eventually, he and the other members of FOXHOUND grew tired of their roles as puppets to the government and attacked Shadow Moses Island.
While on Shadow Moses Island, Psycho Mantis attempted to read Donald Anderson's and Kenneth Baker's minds. When Revolver Ocelot "accidentally" killed Anderson during a torture session, Mantis came up with the idea of tricking Solid Snake into getting the PAL Key from Baker and using the keys to activate Metal Gear REX while making Snake think he was deactivating REX. They made Decoy Octopus disguise himself as Anderson to talk Snake into the act.
As Snake and Meryl Silverburgh made their way through the island, Psycho Mantis managed to control Meryl's mind. He turned her against Snake and tried to make her shoot him, though Snake was able to knock her unconscious. Psycho Mantis then revealed himself and fought Snake himself. On the edge of defeat, Mantis decided to awake Meryl and try to make her shoot herself in the head. However, Snake managed to both prevent Meryl from killing herself and defeat Psycho Mantis.
Upon his defeat, Psycho Mantis tells them to continue onto the communications tower and reveals a hidden doorway in the room he fought Snake in. As Psycho Mantis tells them he can read people's minds, Snake takes off his mask. He reveals that all the minds he read contained the same thought—to pass on their DNA. He also says that humans are fated to bring each other pain and reveals he killed his father and burned his village to bury his past. Psycho Mantis goes on to say he and Snake are similar, that he never agreed with Liquid's revolution, and that he just wanted to mindlessly kill people. He then claims that Snake is worse than Liquid himself. He reveals that he read Meryl's mind and that Snake has a large place in her heart.
Mantis asks Snake to put his mask back on to prevent people's thoughts from forcing their way into his mind. Using his powers, he opens the secret passageway that lead to Metal Gear REX's underground maintenance base. Right before he dies, Mantis says that this was the first time in his life that he had used his power to help someone, and that it felt kind of nice.
Metal Gear Solid 4: Guns of the Patriots
When Liquid Ocelot was building up his PMC armies, Mantis's psychic remnants were somehow harnessed with nano-machines. Liquid wasted no time putting Psycho Mantis's harnessed psyche to use, with it playing a vital role in the creation of the Beauty and the Beast Unit. His psyche was then integrated into Screaming Mantis, and she was then used as a medium to control other Beauty and the Beast members and PMC soldiers. In reality she is only able to do so by manipulating the nano-machines inside their bodies.
In 2014, after Snake infiltrates Liquid Ocelot's Outer Haven he is confronted by the final member of the Beauty and The Beast Unit, Screaming Mantis. After defeating her Beauty form, Screaming Mantis's suit reforms and floats in the air, with Psycho Mantis's spirit appearing behind it. Psycho Mantis once again shows Snake his telekinetic powers. If the player is using a DualShock 3, he cheers about vibration being back, otherwise, he complains that his powers aren't working. Afterwards, The Sorrow intervenes and sends his ghost to the grave for good.
- The battle with Psycho Mantis is widely known for him "displaying" his mental powers. This includes making the controller move by activating the rumble feature, making players think the channel has changed by turning the screen to black with the green caption " HIDEO" in the top-right corner of the screen, and reading the memory card, where he comments on the number of saves so far, and comments on the saved games, first on their genre, then on specific examples. In the original, Mantis mentions Azure Dreams, Suikoden, Castlevania: Symphony of the Night, and Vandal Hearts (plus Policenauts and Snatcher in the Japanese version). He references Super Smash Bros. Melee, Eternal Darkness: Sanity's Requiem, Super Mario Sunshine, and The Legend of Zelda: The Wind Waker in the Nintendo Gamecube remake.
- The fight against Screaming Mantis in Metal Gear Solid 4 is designed to play off people's memories of fighting Psycho Mantis in MGS, right down to the music being a recreation of Mantis Hymn from the original MGS Soundtrack. After Screaming Mantis screams "Blackout!" the screen turns to black and displays a green caption saying "HIDEO2". If the player switches the PS3 controller over to Controller Port 2, Snake will call Otacon saying that he can't move, with Otacon telling him that the trick won't work this time, much to Snake's chagrin. Roy Campbell also suggests that Snake try either swapping controller ports or destroying the mask on the bust of Mantis's face, but Rosemary and Snake rebuke him, stating that neither of those strategies is applicable in the situation. After the battle, when Mantis himself appears, he attempts to read the memory card once more, but fails due to the PS3's hard-drive-based memory system. He also tries to repeat his controller-moving trick, but is unsuccessful due to the lack of rumble feature in the SIXAXIS controller. Enraged, he disappears. However, if the scene is played with a DualShock 3, Mantis will perform the trick successfully and gleefully declare that vibration is back before disappearing.
- After the fight with Psycho Mantis, he will state, that he is "unsure whether or not their futures ( Snake & Meryl) lie together." This could be a reference to the fact that the game has two endings; one where Meryl lives and one where she dies.
- Psycho Mantis is also mentioned in Super Smash Bros. Brawl. Roy Campbell can feed Snake data on Ness if he uses his Codec taunt. During the talk, Snake will recall his encounters with Psycho Mantis, to the point of even asking if Ness can also read minds. Campbell assures him that Ness is "a good kid" and would not use telepathic powers to scan Snake's mind against his will, whether he had such powers or not.