After Luke Skywalker helped his father to defeat Darth Sidious and return to the light side in Return of the Jedi, he travelled the galaxy to search for ancient Jedi temples and artifacts. During his travels, Luke Skywalker discovered a lot of information about the previous history of the Jedi Order and some of its fiercest enemies, like Darth Maul. Luke Skywalker knew about Darth Maul’s fight with Qui-Gon Jinn and Obi-Wan Kenobi on Naboo, Duel of the Fates, and his take over of the Shadow Collective and Crimson Dawn in the Clone Wars Season 7.