All Verne tells us about Nemo (in Mysterious Island) is that he was an Indian prince named Dakkar who took up arms against the Raj, eventually becoming a renegade. The details re: how he subsequently wound up behind the wheel of the Nautilus are vague. Disney's screenwriters brought a lot to the party in `54. Vulcania, Rorapandi, the death of Nemo's family, the "prison escape" story structure, the interplay between Nemo, Ned Land, Conciel and Arronax... all Disney. If one were starting from scratch with a prequel/ sequel its a pretty blank slate, at least as far as Verne is concerned. Interestingly, Verne's original intention was for Nemo to be a Russian who ran afoul of the British during the Crimean War. Verne's publisher, Hetzel, took issue with this owing to France's dodgy relations with both England and Russia at the time. Verne, pissed off by what he deemed to be censorship, decided to keep Nemo's backstory a mystery. It was not until Mysterious Island was published several years later that we are told of Nemo's Indian backstory. The irony is, it was Nemo's mysterious origins in the original novel that gave the character his power (kinda like Vader in the original Star Wars). Sometimes the more you reveal about a character the less interesting he becomes (note to Bryan Singer).