According to Wikipedia, the Moonwalk dance, although popularized by Michael Jackson, dates back at least as far as the 1930's. Singer Cab Calloway is cited as being familiar with it back then, but there's no indication he actually invented it himself. So who did invent the Moonwalk?
There is no known inventor of the moonwalk. The moonwalk is a shuffle-step performed backwards and repeatedly, to simulate one walking back.
Shuffle-steps have always been one of the key pieces of African-American dance, and were notably used in the cakewalk, a dance that developed on southern platations in the 1800s following the end of slavery. Being able to perform the shuffle-step in all directions is key for the cakewalk.
The notion of slipping so that one slides backwards, however, has to do with polished dancefloors. The innovation of the cakewalk being performed on polished dancefloors allowed movement that wouldn't betray the footwork. This development led to many of the animal dances (turkey-trot, foxtrot, bunnyhug, grizzly bear) that were introduced at the beginning of the 20th century.