Chiron

During the Golden Age, as the mortals grew in magic and reached their peak, there were those beings that were not like this, and one of those was the Centaurs, who were much like the Satyrs of the Feywild in that time and they were more of a nuisance to the other races with their antics. However, There was one exception: Chiron, an exceptionally wise and much more civilized centaur than the rest of his race. No one, not even the gods, knows why this is; however, what came of it was something special. It is said Artemis would hold conversations with Chiron, who found this company enjoyable, as well as his discussions with Athena and Baldur, one to have intellectual debates and the other to ask Chiron to tutor some of the future heroes he would be creating. A task that Chiron would take to gladly.
During the Dark Age, Chiron would return to his race and teach them how to defend themselves and would try and remain neutral; however, over time, it was noted that Loki would try to turn the Centaurs to the Fallen's side only for his scheme's to be seen through by Chiron and eventually when subtly did not work Ares was sent to make them serve forcibly. Now Chiron, forced to defend themselves, called on the Guardians and formally joined their side, adding the Centuar's strength to the Guardians and thus entering the war alongside many of the heroes he had tutored.
At the end of the Dark Ages, with the erection of the Divine Barrier, it was noted how heavily the death of many of his students and the world itself weighed on him. It is said that Chiron turned to isolation and disappeared from history and everyone. Some still believe he is somewhere on the material plane, remaining isolated, perhaps teaching more pupils or advising those seeking wisdom.