When Bruce Wayne was a young boy, he was forced to watch helplessly as a mugger named Joe Chill mercilessly gunned down his parents, Thomas and Martha Wayne in cold blood. This single act propelled young Bruce to pursue a career in crime fighting. As an adult, he decided that the most effective means of avenging the deaths of his parents, was by becoming a fearsome creature of the night and thus the Batman was born.
For the first few years of his career, Batman operated alone, prowling the rooftops of Gotham City, but on one fateful evening, he watched history repeat itself. A gangster named Boss Zucco murdered John and Mary Grayson, leaving their young son, Dick, an orphan. Bruce Wayne took Dick in, and trained him in the ways of crime-fighting. Dick became the flamboyant Boy Wonder known as Robin.
Batman and Robin operated as a solid team for many years. Eventually though, Dick grew up, and decided to retire his costumed identity as Robin. He then moved to Bludhaven to become his own superhero known as Nightwing, after he had traveled the world, following the footsteps of his master. Even so Nightwing was still a very loyal and trustworthy ally of Batman.
At the same time, Batman had adopted another young sidekick known as Batgirl. Barbara Gordon, who was the commissioners daughter was a loyal ally to both Batman and Robin before her run in with the Joker, Paralyzing her. Even so she continued to act as an operator for Batman while under the alias, Oracle. Eventually Batman adopted Jason Todd as the next Robin until he was too captured by the Joker, this time killing the young Robin.
After nearly giving up hope on allowing anyone else to run alongside him, Batman is confronted by Tim Drake who wished to become Robin, he proved himself and became the new Boy Wonder. During this time, Jason reappeared, reborn as Red Hood, an anti hero to Batman but still an undying member of the Batfamily, literally. Other anti-hero's such as Catwoman and Huntress were also common allies to Batman, for their own goals of course.