Which game was the first Mortal Kombat crossover with DC Comics characters?

Mortal Kombat vs. DC Universe was the first Mortal Kombat crossover with DC Comics characters.

Released in 2008, the game combines Mortal Kombat fighters with superheroes and villains from DC Comics. Its roster includes characters such as Batman, Superman, Wonder Woman, The Joker, Scorpion, Sub-Zero, and Liu Kang. The story explains the crossover through a merging of the Mortal Kombat and DC universes caused by an unusual cosmic event.

The game was developed by Midway Games and used a less graphic presentation than many mainline Mortal Kombat titles because of the involvement of DC characters. Its success helped lead to the creation of the Injustice series, although Injustice is a separate fighting-game franchise. Mortal Kombat vs. DC Universe is therefore the crossover title, not an Injustice game.