Three times, Holyfield, Tua, and Foreman.
http://boxrec.com/boxer_display.php?boxer_id=1137

I think if he can get REAL serious, and gets back in the shape he was in 10 years ago he might have a shot.
I think Holyfield Moorer II would be an entertaining fight!
(I mean Holyfield Mooer III, Thanks CJM for catching the typo!)