Christopher Boykin, a star of the MTV reality shows “Rob & Big” and “Rob Dyrdek’s Fantasy Factory,” died on Tuesday. He was 45.

A spokeswoman for Mr. Boykin confirmed his death but said the cause had not yet been determined.

Mr. Boykin’s former wife, Shannon Turley, told the television show “Entertainment Tonight” that he died at a hospital in Plano, Tex., and that he had been in the hospital several times over the past year for treatment of congenital heart failure. Doctors had thought that he most likely needed a heart transplant, she said.

Mr. Boykin, known as Big Black, was the professional skateboarder Rob Dyrdek’s bodyguard and buddy. On “Rob & Big,” the duo, mismatched in size and disposition, shared a house in the Hollywood Hills. It was broadcast for three seasons, 2006 to 2008.

The show followed them in their day-to-day antics — using a net gun to catch people, for example, and buying a miniature horse — with Mr. Dyrdek’s bulldog, Meaty, in tow.