'Jackass' Star Vincent 'Don Vito' Margera Dead

Vincent Margera -- the uncle of Bam Margera who appeared in "Jackass" -- has died ... TMZ has learned.

Vincent became famous for pranks he pulled off with Bam on the TV show and later the "Jackass" movies as well as "Viva La Bam".

It's a double blow for Bam, who lost his best friend and co-star Ryan Dunn, who was killed in a car crash.

Vincent has been struggling with kidney and liver failure for several years. He fell into a coma last month and has been in bad shape ever since.

Bam's mom tells us, Vincent passed away Sunday at 6:45 AM.

Vincent was 59. RIP.