Jason Todd was the second Robin. The first was Dick Greyson, who became Nightwing. Second was Jason Todd. Then the third was Bruce’s son Damien.

Jason was a hothead and often went against Batman’s orders. He ended up getting captured by Joker, who tortured him to death and sent the recorded footage to Batman to taunt him.

Depending on which storyline you follow, Todd was either brought back to life via the Lazarus Pits, (which is the same thing Ra’s Al Ghul uses to stay immortal,) or Joker faked his death so Batman would stop looking for him, then continued to torture him for weeks/months/years afterwards. In either scenario, Jason ends up getting free from Joker, and goes sort of crazy. Either due to the Lazarus Pits, (which has a side effect of driving the user a little more mad every time they use it,) or because Joker tortured him so badly.

He has a brief stint as a new supervillain, using his Robin training (intimate knowledge of Batman’s gear, knowing how Batman thinks, knowing how to fight against Batman, etc) to go up against Batman. Basically, he blames Batman for his torture, because Batman failed to rescue him from Joker. He eventually redeems himself, reconciles with Batman, and becomes Red Hood. Red Hood is sort of a Punisher type character, who has Robin’s training but isn’t afraid to use guns.