Terry Crews has been known to be an avid gamer for quite some time, frequently posting on his various social media accounts about his PC configuration, as well as a hard-driven campaign to voice Doomfist in Overwatch.
Therefore, his involvement in Crackdown 3 makes perfect sense. He is featured heavily in the game's advertising campaign, and according to director Gareth Williams, he "basically asked us, ‘can I be in the game?’ And we were like, ‘yeah, you can totally be in the game.'"
What's more, he originally was simply going to be an NPC with a part in the narrative, but eventually asked if he could be made into a playable character, to which the developers happily agreed.
You can watch the trailer featuring Crews below.