Nick Riviera is a quack doctor, constantly appearing on infomercials
? promising all sorts of bizarre medical offers and turning his operations into a TV spectacle. Riviera has a quasi Eastern-european accent, a medical degree from a community college at which he apparently spent much of his time prescribing "anything I want" to a succession of attractive women back in the 1970's, and a great deal of luck.
He has operated on the Simpson family a couple of times, notably when Homer could not afford a heart bypass from his regular doctor. Lisa attended the live audience(!) for the operation and saved the day by guiding the obviously clueless Dr. Riviera through the operation.