"He can slide form chilling charm to fervent rage in an instant. He may be handsome, intense, intelligent, cunning and mercurial, but don't let that fool you -- he's capable of anything," NBC said of Welliver's character named Ronald Booth, who will be making his appearance on the 18th episode of the currently ongoing fifth season.
'I was just so unhappy and it was my dream job and I was miserable and I had to go,' the actress said.
Booth will have a connection to star Tracy Spiridakos' character Detective Hailey Upton.
"Upton was involved with him in a prior undercover case, so she's dusting off an old cover to try to take this guy and his crew down, and it digs up a lot of bad memories," showrunner Rick Eid said to Entertainment Weekly. "She puts herself in sort of a dangerous position, and her partner and friend, Halstead (Jesse Lee Soffer), is there to try to help her."
Chicago P.D. is set to return to NBC on Feb. 28. Following the midseason return, the series will celebrate its 100th episode with a two-part crossover event with Chicago Fire. Welliver's episode will debut later in spring.
Welliver, who currently headlines Amazon's police series Bosch, is known for starring in Lost, The Good Wife, Sons of Anarchy and Deadwood among other television shows.
Chicago P.D., Midseason Premiere, Wednesday, Feb. 28, 10/9c, NBC
By Wade Sheridan
Originally published in UPI Entertainment News.