Gray was with the Longhorn staff less than a month.
"I am excited to have this opportunity," said Gray through a statement. "I have known Mike for a number of years and if he is a head coach like he was a player or a position coach, we are going to be in great shape, because he has had so much success and everything he does. I am looking forward to really getting to know our personnel on defense and creating a defense that takes advantage of our strengths. I am an old school guy that likes to get after the opponent, but you also have to have the players to that – you can't force those things. Our defense will fit what we can do well.
"I also want to thank (Texas) Coach (Mack) Brown and University of Texas," Gray said. "I know the timing of this isn't ideal, but this was something that I couldn't turn down." Brown said the Longhorns were "disappointed" in Gray's departure.
"But at the same time, we're really excited about the wonderful opportunity he had to be the defensive coordinator of the Titans," Brown said. "It is a chance for him to reunite with a lot of friends he went to the Super Bowl with who came up just one yard short of winning. That's the only place he would have left here for, and we want to wish him the best of luck."
Gray's departure means that Brown will have to hire his seventh assistant coach of the offseason.