Jason Todd (Earth-4678)

"Do I look like Batman to you? Rethink your answer before I fill you up with lead."

- Red Hood, to a Black Mask henchman

Jason Todd was a street orphan who was taken in by Batman, becoming the second Robin. Jason was kidnapped and taken to an abandoned wing of Arkham Asylum, where he was tortured by the Joker, who manipulated him into hating Batman over the course of a year. Joker faked Jason's death by sending a tape to Batman in which Robin was apparently shot and killed. He eventually escaped and began plotting his revenge on Batman for not saving and replacing him, taking on the name of the Arkham Knight.

Years later, Jason returned seeking revenge against the Batman, utilizing advanced technology and resources, he was able to develop high-tech equipment & train a battalion of soldiers. However, Batman finally managed to get through to Jason, which resulted in Jason becoming the Red Hood and assisting Batman in taking down Scarecrow. However, while he was once again aligned with his former mentor in wanting to rid Gotham City of its criminal contingent, Todd's willingness to take lives will forever keep them at odds.

Source

 * https://arkhamcity.fandom.com/wiki/Red_Hood
 * https://dc.fandom.com/wiki/Jason_Todd_(Arkhamverse)