For the reindeer see Blitzen (Robbie the Reindeer)
Donner and Blitzen were the Joker's two minions and minor villains in the Batman: The Animated Series episode "Christmas with the Joker".
On Christmas Eve, they were sent by the Joker to blow up the President's Bridge. They blew up the bridge but Batman and Robin saved the 11:30 train. They returned to base and were sent by the Joker to kill Batman and Robin. They shot what they think is Batman, but it was really a giant teddy bear wearing Batman's cape. The giant teddy bear pinned them down and they were arrested afterwards.