David Innes never became the popu lar character that Tarzan and John Carter (of Mars) did, perhaps because he was too bland; but Pellucidar became a popular setting, and Burroughs wrote a short (for him) series of novels in which the action takes place on Earth's inner world. Even Tarzan makes an appearance (Tarzan at the Earth's Core, 1930), showing off what a real action hero can do to Pellucidar's villains. Crucial to the success of the books is that Pellucidar remains a wonderful world for daydreams, where any reader could become a brave hero or heroine who wins the love of a beautiful or handsome, semiclad princess or prince.