Who is the Arkham Knight's true identity?

The Arkham Knight’s true identity is Jason Todd. In Batman: Arkham Knight, the heavily armed villain is eventually revealed to be Batman’s former sidekick, the second Robin, whom the Joker captured and tortured.

Jason had been presumed dead after disappearing, but the Joker kept him imprisoned in an abandoned wing of Arkham Asylum. There, the Joker manipulated Jason into believing that Batman had abandoned him and replaced him with Tim Drake. The trauma turns Jason against his former mentor, leading him to create the Arkham Knight persona and command a militarized army against Gotham.

The reveal connects the game to Jason’s familiar comic-book history, where he later becomes the antihero Red Hood after being killed and resurrected. In the Arkham series, he first appears as the Arkham Knight before eventually taking on the Red Hood identity. A common mix-up is Tim Drake, who is the Robin active in the game, but he is not the Knight.