Billy Joe Cobra
, real name Baruch Cohen, is the ghost of a former sensational rock star. While the details of his death are never explained, he appears to have died young. Some time after, he started haunting his own home as a ghost.
The Wright family, distant relatives of Billy, moved into the Cobra Mansion not long after, and Billy became best friends with Spencer Wright, his distant cousin. Together, the both of them get prank-style revenge on those who wrong them, work to improve Spencer's image, and sometimes just hang out together in a fit of "bro time".
Overall, Billy's main goal seems to be having as much fun as possible, which causes many problems for poor Spencer to clean up after. However, he never turns his back on a friend when he can help it, and can (usually) save the day.