Chiron was a pretty unusual centaur. Sure, he had the upper body of a man and the lower body of a horse like every other centaur, but unlike the most his species, he was super smart and well-behaved. In general, centaurs were known for being lewd and crude. Take, for example, Nessus, who tried to force himself on Deinara, the wife of Heracles, or the centaurs who tried to molest the bride of Pirithous, Theseus's best buddy. Instead of galloping around and behaving badly like the rest of his species, Chiron spent most of his time educating the young heroes of Greece. Besides Jason, it's also said that Chiron taught Achilles, Peleus, and Asclepius, among others.
Chiron was conceived when Kronos, the king of the Titans, was cheating on his wife, Rhea, with a nymph named Philyra. To fool his wife, Kronos transformed himself into a horse, and so Philyra gave birth to the half-hose, half-man Chiron. The young centaur was later taught by Artemis and Apollo, from whom he learned all kinds of good stuff. Though Chiron was supposed to be good at a lot of different things, it's said that he was especially good at prophecy and medicine.
Although, he was immortal, Chiron died when Heracles accidentally shot him with a Hydra-poisoned arrow. The venom of the Hydra was so painful that the centaur gave up his immortality, passing it along to Prometheus. Instead going down to the Underworld, however, Chiron was placed in the stars, becoming the constellation Sagittarius.
Recently, the character of Chiron shows up in the Percy Jackson series as a teacher at Camp Half-Blood. He also reminds us an awful lot of the centaur Firenze, who teaches Divination at Hogwarts in the Harry Potter series. It seem like even death can't stop this centaur from teaching the budding heroes of the world.