'Superman' Director Richard Donner's Death Certificate Says He Died of Heart Failure

Richard Donner -- the legendary director of "Superman," "Lethal Weapon" and many other famous films -- suffered from heart disease and died of heart failure ... according to his death certificate.

The document says Donner died at his home in West Hollywood on the morning of July 5, and the immediate cause of death is listed as cardiopulmonary failure.

The death certificate lists atherosclerotic cardiovascular disease as an underlying cause of his passing, as well.

On a lighter note ... according to the document, Donner was a film director for 65 years, meaning he started his iconic career in the late '50s.

As we told you ... Donner was one of the most beloved figures in Hollywood who got his big break with 1976's "The Omen," which led to the 'Superman' and 'Lethal Weapon' franchises.

He's also known for flicks like "Ladyhawke," "The Goonies," "Scrooged" and "Conspiracy Theory."