Grantham Coleman has joined the cast of Starz’s Power Book III: Raising Kanan according to Deadline. He is set to play the role of Ronnie Mathis. The season finale of season two aired on Sunday and production on season three has already started. Ronnie is Unique’s older brother, who was recently released from prison. Ronnie’s stoic demeanor belies a shocking ruthlessness. It’s not that Ronnie’s immoral, it’s that he’s amoral, conscienceless, unyielding and vindictive. The series also stars Omar Epps, London Brown, Malcolm Mays, Hailey Kilgore, Shanley Caswell and Antonio Ortiz.