Luther Wainwright was Lisbon's Team new superior replacing LaRoche. He is shown to be quite intelligent but also arrogant when he first appeared in Ring Around The Rosie. Since then, he was a recurring character throughout Season 4 until his death in The Crimson Hat at the hands of Susan Darcy (from the FBI) in a confusion orchestrated by Red John.
Wainwright is shown to be sympathetic and understanding at first, when he allows Jane to investigate a man whom he believes is close to a psychotic break and killing somebody. Once they discover the disturbed man's illegal possession of guns by breaking into his house, Wainwright decides to put a stop to the investigation and arrest him on the charge and recommend counseling as an added precaution. Jane does not agree with this, saying it would be far more thorough to catch him in the act, effectively putting him away for good. Wainwright disagrees and as it turns out Jane was manipulating him into being the final stressor for the disturbed man that pushes him over the edge. Wainwright takes this in stride and tells Jane that from what he has observed so far, Jane shows most of the hallmark signs of being a high-functioning clinical psychopath. He further says he will "adjust accordingly", as he knows what he is dealing with now.
Later episodes show Wainwright being mellow and generally not taking a very active role in Lisbon's cases other than giving them deadlines or incentives for the high profile ones. He even receives the news that Lisbon and her team, at Jane's prodding, deceived him about the death of a famous victim unperturbedly, simply sincerely stating that he hoped the ploy worked.
Wainwright is secretly helping Susan Darcy investigate the Red John murders, after the murder of Panzer and her subsequent realization that Red John may be the actual killer, she requested all the evidence on Red John. Wainwright has provided her with this and has covered it up from everybody in the CBI office including Lisbon and her team, possibly because he suspects someone in the office or because he is suspicious of Jane and the circumstances of Panzer's death. Wainwright has officially fired Patrick Jane from the CBI.
It was in The Crimson Ticket, that Wainwright is shown to have become Red John's 29th murder victim (he was discovered as a stand-in for Red John in the back of the limousine). It is unknown how he got into the limousine but the last person he talked to appears to be FBI Agent Susan Darcy.
In The Crimson Hat, it is stated that he was killed by gunshots from Susan Darcy; rather than being dead before entering the vehicle. (Some Wikia users theorized that Red John killed him before he entered the vehicle, but that theory is proven to be wrong.)