Sagittarius is usually depicted as a centaur holding a bow and arrow. It is one of the largest southern constellations. It is easy to find because it lies on the Milky Way and its brightest stars form an asterism known as the Teapot.
According to the Greek Mythology, Chiron was one of the many centaurs. However, he was different from all of the other centaurs for a number of reasons. One main reason was that Chiron was born half man and half horse, whereas the other centaurs were born of the sun and rain clouds.
One day Chiron was accidentally shot with a poisoned arrow by Hercules. Even though he was a great physician, Chiron could not heal himself. And because he was immortal, Chiron also could not die but he was suffering from the agonizing pain caused by the poisoned arrow.
In order to die, Chiron offered to replace Prometheus who was punished by the Gods for giving fire to man. As Chiron gave up his immortality to release Prometheus from his chains, Zeus king of the gods saw the kindness of Chiron and immortalized him in the stars.