Antero was the scholar/sage that wrote the book "Antero's Bestiary." He was the master of Ewan and used him to gain information for him. He valued history and knowing the many different cultures of the world. Antero was probably trained by Nelarn, but this is just an estimated guess at best. Perhaps, with the many mages listed in the world--Alric may have planned to use such individuals in the reestablishing of the Avatara order.
Antero as an Avatara during the events of Myth 2 Soulblighter--he could use all the same powers as Nelarn.