Francis Albert "Frankie" Stecchino (aka Frankie the Enforcer) is a very large and strong kid at John Adams High. Harley Keiner, the local bully, took advantage of his strength to turn him into his head flunky, alongside Joey the Rat. When Harley got sent to reform school, Frankie revealed his gentle side and became friends with Cory and Shawn.
Seems to return to his criminal ways after reappearing with Joey in Graduation. However, this could just be a non-canon joke for old time's sake as this episode marks the final appearances of both Frankie and Joey.