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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.