By The Nation
A Facebook page set up for the bear had more than 14,000 followers.
Park chief Kanchanaphan Khamhaeng said Charlie was found dead with foam around his mouth, but had shown no sign of illness recently and had eaten well on Monday.
He recalled the bear foaming at the mouth once before, after it was bitten by a centipede, but it had quickly recovered under treatment.
The body was sent to Kasetsart Animal Hospital in Hua Hin for an autopsy.
Charlie was tame enough to be allowed to roam the compound and have its photo taken with visitors.
The bear was rescued as a two-month-old cub from a pack of menacing dogs.
Early on he suffered convulsions because of a brain ailment, which the Kasetsart Animal Hospital vets were able to cure, though the bear continued to need monthly medication.