Barbara Gordon: Daughter of Gotham's corrupt Commissioner, Jim Gordon, she used to be Batgirl until a man whom her father had wrongfully arrested and later falsified evidence to have put in jail shot her in the spine, paralyzing her from the waist down. She is now Oracle, hacker extraordinaire.
Dick Grayson: Orphaned at eight when his parents fell from their trapezes due to the ropes being sabotaged, he followed the men he'd observed earlier, who had threatened the owner of Haley's Circus, and brutally killed them. He was found there some time later by Slade, who took him to the authorities. Dick strongly objected and ran away. Slade tracked him down again, found him having a major freakout, and -- Slade being Slade -- slapped him to get him to calm down. And then gave him a hug and stroked his hair to quasi-apologize for having to slap him. Dick immediately focused all of his post-traumatic stress willpower on Slade, and still does. He is an assassin who goes by Redwing and specializes in knives. He also works with the Batclan.
Tim Drake: Met Dick Grayson when he was three years old and witnessed the Graysons' murders. He ran away from home when he was twelve to go to Batman, whose identity he'd figured out, to join the Batclan and get a chance at Dick. He later killed his parents, who were always flying to other countries and generally never saw their son, and blew up their graves. He goes by Cardinal and is Batman's left hand. He is also completely in love with Dick and makes no secret of the fact that he hates Slade for having Dick's utter adoration.
More biographies to follow.