Jason Todd

"Blindly, stupidly, disregarding the entire graveyards he's filled. The thousands that have suffered. The friends he's crippled.You know I thought...I thought I'd be the last person you'd ever let him hurt. If that had been you that he'd beat to a bloody pulp... If he had taken you from this world...I would have done nothing but searched the planet for this evil death worshiping garbage, and sent him off to h**l!"

- Jason Todd (confronting Batman over letting Joker survive)

Jason Todd was once one of the main protagonist in the Batman comic books, but he was killed by the Joker an was later revived by the effects of Superboy Prime. Because of this he became enraged and took the identity of the Red Hood II.

History
Jason grew up on the streets for a while before he was found by Batman. In the movie he was seen trying to steal the tires off of the BatMoble. After of which he was taken in by the man. He later on became the second Robin. After Jason was killed by the Joker, his ghost told Batman that he was at peace and that he was in Heaven. But this didn't last forever. Because of the effects of Superboy Prime who was attempting to escape from a supposed "paradise". This caused a ripple in reality, which caused Jason to awake inside his coffin. Jason was revived, but his brain was damaged and had no memory of his true identity. He wandered for years until he encounter both Ra's and Talia al Ghul. Both of them took him in. Talia submerged Jason in a Lazarus Pit and re-awakened his all of his memories completely intact. When he found out that the Joker was still alive, Jason was enraged and decided to take on the identity of the second Red Hood, and became one of the scourges of Gotham's underworld.

New 52
During the New 52 relaunch, Jason as Red Hood was placed into his own series Red Hood and the Outlaws where he has formed his own three-man team consisting of himself, Starfire and Green Arrow's former sidekick Arsenal. Also his violent nature has been toned down for the new series as he is not as eager to kill as he had before. He is still viewed as a criminal in the eyes of Batman and his other allies.

Issue 0 of the series does a retelling of Jason's origin which is about the same as before except that since Superboy Prime does not exist in the new continuity, the Lazarus Pit was used to bring Jason back to life.

Teen Titans
Though Jason Todd didn't appear in the TV Show; Teen Titans, he does make a brief cameo, and there has been rumors that one of the villains known as Red X is really Jason Todd behind the mask.

Batman: Under the Red Hood
Jason Todd is the main antagonist in Batman: Under the Red Hood. In this animated film he seeks a bloody revenge against the Joker for nearly killing him as well as trying to force Batman to kill - an act Batman flat out refuses to do despite Joker's absolute joy at how he broke Todd and made him a killer. The animated feature is basically a retelling of the comic book arc but has a few differences, as can be expected due to the difference in media.

Young Justice
Although you do not see Jason appear in Young Justice he is shown breifly in a few of the episodes. He is seen with the other members that have passed away, one of the holigrams that is left for them to respect those that have passed. There is a speculation that at some point he will in the show as "The Red Hood". However, as of Endgame, most of that has been cancled in the minds of many fans for the reason that Young Justice is not supposed to be returning with a third season.