His name is Qui-Gon Jinn. Was Qui-Gon Jinn. Among his Jedi peers he was an outcast despite being a model practitioner of the Force, for embracing ideas the Council was slow to accept, such as the prophecy of the chosen one who would bring balance to their mutual power source. Balance, you see, was necessary, because for untold generations and throughout innumerable conflicts large and small, the Jedi had rivals in the Sith.
Qui-Gon discovered the chosen one, a little boy named Anakin Skywalker, living on the desert world of Tatooine. Mindful of things but also wary, he set about a course that would force both his allies and enemies into fulfilling the prophecy. During these efforts he was struck down by the Sith apprentice Darth Maul, or that's certainly what Qui-Gon's own apprentice Obi-Wan Kenobi believed.
To cover his mistake, once he realized what had actually happened, Kenobi began weaving an incredible web of lies. First, he told the Council that Qui-Gon Jinn was dead. Then he convinced his superiors to take on Skywalker as his apprentice, someone they all well-knew enticed the Sith master Darth Sidious to seek for his own purposes. Finally, when Kenobi and Skywalker clashed in mortal combat on Mustafar, the chosen one was fatally wounded and left for dead by Kenobi, only to be retrieved by Sidious and placed in what would be the iconic outfit of Darth Vader.
Since the Jedi themselves became all but extinct around that time, it was easy for Kenobi's lies to be accepted, most of all by Skywalker's own son, whom Kenobi helped raise, once more on the desert world of Tatooine.
The truth, of course, is that it was Qui-Gon Jinn encased in the life-preserving apparatus concealed in the black robes and helmet of Darth Vader.
Qui-Gon realized he would never be able to convince his Jedi peers that he was right about the prophecy. It wasn't a matter of faking his death so much as allowing himself to fall into the clutches of the Sith. Darth Sidious eagerly embraced this latest Jedi defector, as he had done with so many before, never suspecting for a moment that Qui-Gon would be the one to finally bring his reign of terror to an end.
When Kenobi clashed with Skywalker, Darth Vader was indeed there. The truth, from a certain point of view, as Kenobi would later try to explain to Skywalker's son, is a malleable thing. He first explained how Vader and Skywalker were two separate people, and then the younger Skywalker was told by Vader himself that Vader was Skywalker. Except, of course, that was a lie to protect Qui-Gon himself. Serving under Darth Sidious for all those years, he had begun to fear, warped him. He was no longer convinced of his own ideals, and didn't trust himself anymore, either.
He needed Skywalker's son to push him back to the path he'd set himself on a long time ago.
So he needed a lie. He would become the boy he'd failed all those years ago, the one who died before the prophecy could be fulfilled. Qui-Gon had seen a vision of the future. He knew he'd rushed to confront the Sith threat too soon, pushed the boy too fast.
As he told a Gungan once, "There's always a bigger fish." Sacrifices are necessary, so long as you fight for something bigger than yourself. In the end, that's what Qui-Gon Jinn did.