Former WWE Wrestler Sir Mo Dead at 58

Sir Mo -- a former WWE tag team champion -- has died ... TMZ has learned.

Gerald Horne -- Sir Mo's brother -- tells us the former wrestling star died Sunday night at a Texas hospital.

Sir Mo -- who's real name is Bobby Horne -- had been battling kidney issues for a long time, which lead to him being hospitalized for the past couple months.

We're told Sir Mo's condition recently declined after he was diagnosed with pneumonia and a blood infection while in the hospital.

Sir Mo began his pro wrestling career in 1991 ... and two years later signed with WWE alongside his tag team partner, Nelson Frazier. The duo became known as "Men on a Mission" ... winning a WWE tag team title in 1994.

He was 58.