Basil Karlo (Earth-5728)

"You weren't even supposed to be in here, Karlo. Why side up with the Joker? Easy... The role of a lifetime!"

- - Batman and Clayface

Basil Karlo was an actor who starred in multiple horror movies which were famous on Gotham City. After discovering one of his classic roles in The Terror would be remade with another actor in the lead role, he cosplayed as the movie's antagonist and started killing the entire cast before being stopped by Batman and Robin. After stealing experimental compounds studied by S.H.I.E.L.D., he injected himself with them and became the creature known as Clayface.