Robert F. Chew -- best known for playing Proposition Joe on "The Wire" -- was found dead yesterday in his apartment in Baltimore ... TMZ has learned. 

According to the coroner in Baltimore, Chew died of cardiovascular disease. "Morbid obesity" was listed as a contributing factor.

Chew had very little acting experience before "The Wire" or after. He was on the cult HBO show -- which took place in Baltimore -- for five seasons. 

Jamie Hector, who played Marlo on the show, tweeted this afternoon, "I didn't want to believe this #RIP Robert F Chew, Prop Joe will always be remembered Robert Chew will always be loved and missed!"