Alpha Centauri is a hermaphrodite hexapod, properly an "it" although most people seem to prefer calling it "he". This is a striking contrast with Alpha Centauri's high-pitched voice! His most immediately-obvious feature is his head, which entirely dominates his body and is covered in red veins. At the front of his head is one large lidded eye. The rest of Alpha Centauri's body is long and straight, mostly green but with a patch of yellow in the front, ending in a slightly flared base. From his sides hang six black arms which culminate in claws. This top-heavy body design means that Alpha Centauri is unable to right himself if he falls; his arms are apparently pretty useless for pushing him off the ground, and as they are all on one part of his body, he has nothing to stand on. For clothing, Alpha Centauri always wears a curtain-like yellow cloak around his neck.
A very sweet creature by nature, Alpha Centauri is very much a coward by instinct and does not like unpleasant things at all. He is afraid to stand up to people, and will pretty much do anything they ask. But he possesses a strong moral core, and while he can face death for himself, he cannot stand by and let violence be inflicted on fellow creatures. While this does not mean that he will physically protect them, he will do everything in his power to be sure that they are not harmed.
Alpha Centauri and the Doctor consider one another to be very good friends. When they first meet, Alpha Centauri is his planet's ambassador to Peladon, hoping to persuade the king to join the Federation. By their next meeting - at which they are both overjoyed to see one another - Alpha Centauri has become a Federation ambassador (possibly assigned to Peladon). Presumably this is where he remains.
