Before Crime FightingEdit
Not a lot is known about Bat-Hound's backstory except that Batman found him in a sewer.
He was first introduced in Lego Batman - New Sidekicks along with Batgirl as Batman's clue-finding dog sidekick. For some reason, Batman had completely neglected training the dog, leaving the mission to Robin.He eventually proved himself too much for Robin to handle when he ambushed and began humping him. Finally, Robin went to Alfred for advice. Instead he was given a needle to stick in the dog's anus to kill it. Just as Robin was moving in for the kill, Batman called Robin, explaining his situation of being captured by Mr. Freeze and asking for both of their's assistance. When Robin and Bat-Hound arrived, Bat-Hound immediately started humping Mr. Freeze before Batman killed him. It is unknown if he was impaled on an icicle, frozen to death, crushed or survived the moon crashing down on earth. He has not been seen since.
Bat-Hound is a regular Lego-dog with a Batman logo sticker on both sides of his body.