Melvin Williams, who plays "Deacon" (the guy giving advice to Cutty in the church) was one of two real-life inspirations for Avon Barksdale; Williams served 34 years in prison, for crimes related to being one of Baltimore's major heroin dealers in the 60s and early 70s, and was arrested by 'The Wire' co-writer Ed Burns (who, before writing for TV, was a BPD detective, then school-teacher, partially inspiring the character of Roland 'Prez' Pryzbylewski). Williams died in 2015.
Gbenga Akinnagbe joins the cast in the role as Chris Partlow. Akinnagbe had previously appeared in an episode in Season 1, albeit playing a different character.