Ron Lester -- the lovable heavyset man in "Varsity Blues" -- has died ... TMZ has learned.

The man famously known for playing Billy Bob in the 1999 football flick had been hospitalized in Dallas for roughly four months. His health had been in a steady decline but turned for the worst Friday.

We're told Lester requested to be taken off life support and passed around 9 PM central time. His fiancée was by his side.

Lester -- who also appeared in "Not Another Teen Movie" and "CSI: NY" -- battled with liver issues as far back as November. We're also told he suffered from kidney problems.