Sylar

Sylar is a serial killer who sometimes removes the brains of his victims, primarily those he believes to be evolved humans. Chandra Suresh identified him as Patient Zero in his research. Before adopting the name Sylar, he was known as Gabriel Gray.

The episode "Six Months Ago" reveals that Sylar's real name is Gabriel Gray, a highly talented watch repairman. He encounters Chandra Suresh, who tells Gabriel that he may be an evolved human with superhuman powers. Gabriel eagerly submits to testing. After being rejected by Suresh because the test results are indeterminate, Gray contacts another person on Suresh's list, Davis. Gray discovers that he himself has the power of intuitive aptitude, and murders Davis for his telekinetic powers. After returning to Suresh, he becomes "Patient Zero", and continues to work with Suresh until Suresh realizes that Sylar is murdering the people that they meet. He kills Suresh soon after.

Sylar is first mentioned in the series as a mysterious serial killer sought out by the FBI, whose existence is completely speculative. Appearing as shadowy figure, he attempts to obtain Molly Walker's power after failing the first time, obtains the power of Charlie Andrews, and attempts to obtain Claire Bennet's regenerative abilities, but is stopped by Peter Petrelli. He is greatly injured and is captured by Eden McCain and the Haitian to be experimented on. After various experiments, Sylar manages to escape, but he is again repelled from an attempt to obtain Claire's power.

Remembering Suresh's list, Sylar makes his way to Zane Taylor, and by posing as the person Zane was expecting, Mohinder Suresh, he kills him and obtains his power. After Mohinder arrives, Sylar poses as Zane, and convinces Mohinder to take him to help convince other people with special abilities that Mohinder’s research is real. After meeting and obtaining enhanced hearing from a woman named Dale, Mohinder discovers Sylar's identity and manages to incapacitate him with drugs. After experimenting on Sylar to create a new list of people with special powers and attempting to kill him, Mohinder is captured. After Peter shows up and is temporarily killed by Sylar, Mohinder knocks him out, but ends up leaving Isaac Mendez's address on the ground.

After meeting Isaac, and being told that his fate is to die at the hands of the other heroes, he takes Isaac's power to paint the future. He soon finishes a painting depicting himself about to kill and absorb the power of the radioactive Ted Sprague, and believes himself to be the "exploding man". Believing that only those that "don't deserve" their powers are the ones that need to die, he doesn't want to kill innocent people. After attempting to confide in Mohinder, he returns home to his mother in the hope that she will tell him that it is fine not to be special and live as a normal watchmaker. She tells him that he can be anything, including the president, causing him to demonstrate his powers and accidentally injure her. This causes her to panic, which eventually leads to her death, and Sylar deciding that his path is correct.
 
Sylar being impaled by Hiro Nakamura.

After absorbing the radioactive powers of Ted, Sylar paints a picture of himself facing off against Peter Petrelli at Kirby Plaza. Realizing Peter is part of his final destiny, Sylar prepares to hunt him down. Before he can leave, Ando Masahashi arrives to kill him, though Ando is easily thwarted. After Sylar discovers the comic depicting his death at the hands of Hiro Nakamura, Hiro appears and rescues Ando. Sylar sets off for Kirby Plaza to wait for Peter. After a struggle involving Sylar, Peter, Matt Parkman, and Niki Sanders, Peter begins the process of exploding, showing Sylar that he is not the exploding man. Soon after, Hiro arrives and stabs Sylar as the comic depicts, which causes him to collapse.

Generations

Sylar is rescued by Candice Wilmer, who uses her powers of illusion to make Sylar disappear. After undergoing eight surgeries, he eventually awakes and realizes that he cannot use his powers. Though Candice promises that they will come back eventually, he kills her and attempts to absorb her power in order to start over. After realizing that it also doesn't work, he attempts to leave, though he realizes that he is in the middle of a dense jungle in Mexico. After wandering for three days, he is rescued from the brink of death by the passing by Maya Herrera and Alejandro Herrera. He introduces himself using his real name, and eventually finds out that they are in search of Chandra Suresh to help control Maya's power. He tells them that he knows Suresh, and that he will take them to him.

He continues to travel with them, and while Alejandro becomes more distrustful of Sylar, Maya becomes more trusting of him. After teaching Maya to control her powers, he convinces her that her brother hates her and that in her heart she wanted to see his wife dead. Convincing her to send Alejandro away, Sylar is eventually confronted by Alejandro, he kills him, but states that he would have let Alejandro go had he not come back. Soon after, Maya confesses her love for Gabriel, and they reach Mohinder's apartment. Sylar attempts to obtain a cure for his condition, later revealed to be the same strain of the Shanti Virus which Niki was infected with. Upon finding that Sylar cannot use any of his obtained abilities, Mohinder attempts to kill Sylar, causing Maya to find out Sylar's true intentions. Sylar then takes Maya, Mohinder and Molly hostage, and later forcing Mohinder to give Sylar the cure. He escapes with the cure, however injured due to an attack from Elle.

Villains

At the start of Volume Three: "Villains", Sylar injects himself with the cure, healing his wounds and apparently regaining use of his powers. He tests out his telekinesis by summoning a can to his hand, ominously remarking, "I'm back."