Jason Todd/Red Hood
Jason Todd was the second Robin. He grew up as a street kid whose father was in and out of prison. He got good at figuring out how to survive alone. He began to do petty crimes to make ends meat. One day he was caught by Batman trying to steal the tires off the Batmobile. Jason was unlike his predecessor, Dick Grayson. He was angry, used excessive force, and would often disobey Batman. This all lead Bruce to benching Jason for a time. Bruce’s intent was to get Jason some help so that he could deal with his demons before allowing him to resume field work. During this time Jason found that his mother was still alive in Europe. He stole Bruce’s credit cards and went abroad to find his mother as Robin. Bruce would also go to Europe in pursuit of the Joker. This would force Bruce and Jason to cross paths abroad, and Bruce allowed Jason to temporarily retake the mantle of Robin during his mission. It turns out that Jason’s mother was working with the Joker and she betrayed Jason giving him to the Joker. This would lead to Jason’s torture and ultimate murder.
This wasn’t the end of Jason’s story though. Depend on what version you read, Jason was either brought back as an offering to Bruce by Ra’s Al Guhl who would use the Lazarus Pit or by a massive punch by Superboy Prime that would break the time and space continuum. Regardless, Jason would come back, and he would be angry that even after the Joker murdered him, Batman had not killed him. Jason would spend the next few years recreating the traveling that Bruce Wayne did when he began his training as Batman. After he completed this training, he would go back to Gotham to reveal that he was alive and would cause hell as a nemesis to Batman for a short time.
Jason would eventually come back into the fold and begin working with Batman again directly. They clearly have some issues to work out still, but they trust each other.