After Revenge of the Sith and the conclusion of the prequels, the idea of new Star Wars content wasn't something that was even on many people's radar, but Star Wars was alive and well; in fact, some of the best Star Wars stories ever were being told in animation through The Clone Wars animated series. Bringing on Dave Filoni as supervising director, George Lucas used The Clone Wars to bridge the gap between Attack of the Clones and Revenge of the Sith, detailing more of Anakin's path as a Jedi and, according to many fans, "fixing" the prequels in the process by making Anakin a more sympathetic character.
One of the most significant events in The Clone Wars was the return of Darth Maul. While he originally appeared to fall to his death - after being cut in half by Obi-Wan - at the end of The Phantom Menace, The Clone Wars revealed that he was able to use his pain and rage to wrap himself in dark side energy and preserve his life, but he slowly lost his mind in the intervening years until he was eventually discovered.
He's brought to the Nightsisters on his homeworld of Dathomir, where his mind is repaired and he's given mechanical legs, only to find the galaxy had moved on without him. His master had taken on a new apprentice, Dooku, who was now leading Separatists in the Clone Wars. His destiny had been stolen from him, and he set himself on getting revenge on the one he found responsible - Kenobi.
None of their run-ins in that series resulted in any sort of final resolution. In fact, the last time Kenobi saw Maul, he had taken over Mandalore and murdered his close friend, and former romantic connection, Satine Kryze - right in front of him. Needless to say, they both have scores to settle - and they're finally about to do so in the next episode of Star Wars Rebels, 'Twin Suns'.
After spending most of season 3 trying to track down Kenobi, Maul is finally about to locate the Jedi Master in his exile on Tatooine, but that wasn't originally where the former Sith's story was supposed to go. In an io9 interview with Dave Filoni, the Rebels producer spoke to Maul's intended end:
“Originally Maul perished in the season two finale where he returned. It was a one-off appearance... So originally in that episode you were gonna get Vader fighting Maul, Vader would have killed Maul, and then fought Ahsoka... It just became unwieldy... There were too many storylines, and there isn’t enough emotional material between Vader and Maul. It’s more of a fan fiction fun thought that they fought. The emotional drama was really between Vader and Ahsoka. So we decided to let Maul live.”
While Vader vs Maul would have been an epic showdown, the decision to focus on Ahsoka vs Vader really paid off. Not only because it delivered one of the most emotional moments of the entire saga, but because it freed up Maul to fascilitate what we've seen in season 2: pushing Ezra to the dark side, providing a link from Sabine to the darksaber, and, soon, facing off against Obi-Wan Kenobi one last time.
While he hasn't actually killed any Sith Lords (now that we know Maul survived), Obi-Wan has actually had more confrontations with the Sith than any other Jedi we see in Star Wars, even declaring in Revenge of the Sith that "Sith Lords are our specialty". Filono references this quote, saying “You always felt Obi-Wan had this great track record of taking out a Sith Lord in the past... We wondered, [by bringing back Maul], did we rob him of what he was able to accomplish?”
Outside of Anakin killing Dooku, then later killing Palpatine, Obi-Wan was the only Jedi to be shown killing a Sith, only for it to be revealed that Maul survived. Does this diminish Obi-Wan's victory, or "rob him" of his accomplishment as Filoni says? Regardless, the saga of Kenobi and Maul appears to finally be coming to a close. With a gap of nearly two decades between Revenge of the Sith and A New Hope, there's been a dearth of Obi-Wan stories, outside of a few brief snippets involving him meditating and watching over Luke. Not only does this wrap up one of the biggest loose threads of the saga, but it will provide fans of Obi-Wan one of the biggest looks at the Jedi Master's life on Tatooine yet, in what Filoni has said is a valuable addition to the story.