Pariah: The Lives and Deaths of Sonny Liston « Movie from 2019

Overcoming the seemingly insurmountable odds that life threw his way, Liston became the heavyweight champion of the world when he knocked out Floyd Patterson in 1962.

Just eight years later, his wife finds him dead in their Las Vegas home from a supposed heroin overdose. Suspicion as to the cause of death pervaded among those that knew him.