Mace Windu was a Jedi Master who fought in the Clone Wars. He is the only Jedi known to have wielded a purple lightsabre. He was also the first to suspect Palpatine of being the Sith Lord behind the Clone Wars. It is thought that he discovered the force-sensitive child that would become Obi-Wan Kenobi while on a mission to the planet Alderaan. He was a member of the Jedi Council. He became incredibly popular after killing Jango Fett.
While he defeated Darth Sidious in a lightsabre duel, he was subsequently killed when Anakin Skywalker distracted him.
Mike Wong's Commentary
Mace Windu's death sealed the fate of the galaxy, and in many ways it was caused by his own character flaws. He had made little effort to conceal his dislike and distrust of Anakin Skywalker ever since Anakin was a little boy, and Anakin is a character who is driven not by loyalties to ideology, but by loyalties to people. In essence, in the most critical moment of the entire six-film Star Wars saga, Anakin Skywalker found himself facing two men: one of whom who had befriended him since childhood and the other who had disliked him, distrusted him, and tried to block his path at every conceivable turn.
In short, while Mace Windu may have been the ideal Jedi to fight Emperor Palpatine, he was the worst possible Jedi to keep Anakin from making the wrong decision. Windu's strict and uncharismatic character, who seems so arbitrary and unimportant in the first two movies, turns out to be a remarkably important character to the fate of the galaxy. And while some disliked the character for his cold and aloof manner, it was precisely those qualities which made him so crucial to Anakin's fall. And to make a bad situation worse, Windu had been planning to forcibly remove Palpatine from power even before he had learned that Palpatine was a Sith Lord: a fact that undoubtedly influenced Anakin when Palpatine accused Windu of being a traitor.