Pellucidar is a fictional Hollow Earth invented by American writer Edgar Rice Burroughs for a series of action adventure stories. In a crossover event between Burroughs' series, there is a Tarzan story in which the Ape Man travels into Pellucidar.
Edgar Rice Burroughs (September 1, 1875 – March 19, 1950) was an American writer best known for his creations of the jungle hero Tarzan and the heroic Mars adventurer John Carter, although he produced works in many genres.(Wikipedia)