Comedian James Gregory -- known for dubbing himself "The Funniest Man in America" -- has died ... according to a post from his family.

The post -- made on Gregory's official Facebook -- says James passed away Thursday from cardiac complications.

James took up comedy in the early '80s when he was 36 after years of working as a salesman ... and, he became the first comedian to take the stage at the legendary Punchline club in Atlanta. While he was known as a Southern comedian, he traveled all across the country performing shows for the next four decades.

His biggest claim to fame came when he dubbed himself "The Funniest Man in America" in the '80s ... and, later he took the URL domain "funniestman.com" -- cementing himself in his fans' minds as the funniest man.

In fact, it seems JG wanted to keep people laughing for many years to come ... because he had two shows in Hoover, Alabama scheduled for Friday and Saturday.

Fans of his can learn even more about him in his upcoming autobiography, "A Bushel of Beans and a Peck of Tomatoes: The Life and Times of 'The Funniest Man in America'", set for release in November.

Gregroy's survived by his three nieces and other extended family. He was 78.

RIP