I’ll be quick, last night at the Video Game Awards this teaser was shown:

Which confirms rumors from earlier this week that hinted at the inclusion of the God of War character in the new Mortal Kombat.

Also earlier this week there was a mishap at the official MK website which granted users access to a directory list of sound files, this YouTube video sums it up quite nicely:

Keep in mind that not always sound files end up being in the game, so this is not a 100% confirmation of the characters, only time will tell.

EDIT: More characters confirmed: Ermac and Sindel!
EDIT2: Even more characters: Jade and Goro!