Jason Todd (aka Robin) was a vigilante and sidekick of Batman, preceding Damian Wayne. He was killed by Joker some time during Batman's earlier years.
Jason Todd was found by Batman and was groomed to become the vigilante Robin. After a period of time, however, Jason died and was presumably replaced by Batman's son, Damian Wayne, as his successor.
- The fact that Joker is aware of Jason Todd's death may allude to his involvement, much like his death in the comics.
Behind the scenes
He is mentioned by Joker in the episode "All the Best Inmates Have Daddy Issues". It is unknown whether he will make an appearance as Red Hood in the future.