Ridley (Metroid)
Often considered one of the most memorable Nintendo villains, Ridley has been a mainstay of the series, having appeared (through various incarnations) in almost every "Metroid" game to date (all but "", "Metroid Prime Hunters" and ""). He has also appeared in the "Super Smash Bros." series, however, he had not been made a playable character until "Super Smash Bros. Ultimate" in 2018, making it also the first game overall to have Ridley as a playable character.
Matrix (novel)
It features the Seventh Doctor and Ace. It also includes appearances by the Wandering Jew and Jack the Ripper. Part of it is set in an alternate timeline, featuring parallel universe versions of Ian Chesterton and Barbara Wright. The villain is the Valeyard.