No one knows what Kentauros looked like. (Indeed, few people seem to know who Kentauros is.) Neither Edith Hamilton nor Bulfinch's compendia of Greek mythology include accounts of the origins of centaurs, and when other mention it, it usually to say that centaurs were born when the human Ixion lay with a cloud in the shape of Hera. The moral of that story -- that Ixion's unnatural lust for the goddess, compunded by the fact that it was in fact a cloud (or, in other accounts, the cloud nymph Nephele) with whom he slept, could only produce monsters -- is echoed in other myths, such as that of Pasiphae and the Minotaur. But in the earliest account I have found -- that of Pindar, who precedes just about everyone except Homer and Hesiod -- Ixion's union with the simulacra of Hera produced Kentauros, called a monster but otherwise undescribed. It was Kentauros's mating with the Magnesian mares that produced the race of hippocentaurs, the half-horse, half-humans known today simply as centaurs.
Here is Pindar's account, from Pythian II
Far were the Graces when Cloud
Bore him a monstrous issue,
She like nothing, and like nothing It;
Which found no favor among men, nor in
The company of the Gods.
She nursed It and called It Kentauros: and It lay
With the Magnesian mares on Pelion's foot-hills.
And a race was born
Prodigious, in the image of both parents,
Their nether parts of the mother, their father's above.
(tr. C.M. Bowra, from the Penguin Odes
The word kentauros
seems to mean bull-slayer. (My ancient Greek is very weak but consulting Donnegan seems to confirm this.) One can see what Pindar was getting at: the union of a human and a nymph could only produce something human in appearance; but if its monstrous nature (a produce of its monstrous conception) led it to mate with animals, the resulting offspring would partake of both parents.
But of Kentauros nothing else (that I can find) was said by any ancient source. Pindar's "far from the Graces" means that its birth was unblessed (the more literal Myers translation available from Perseus says "without favour of the Graces"), so that although he was nurtured by his mother, his cursed nature was recognized -- by a validating source whose authority was beyond appeal -- even before his birth. From this, we gather, came a life of solitude, including erotic solace found only among a herd of horses in Thessaly.
A potentially interesting figure, Kentauros. But I have never read anything else about him.