Eldor is the name of a planned character for the cancelled The Powers of Grayskull toyline. In the planned storyline, Eldor was He-Ro's mentor and the guardian of the Book of Living Spells.
Origin #1 (MVCreations 200X Comics):
Eldor has a cameo in issue #5 of volume 3 of the MVCreations comic book as part of the Council of the Wise.
Origin #2 (MOTUC Bios):
The great sage and wizard of Preternia, Eldor arrived at a burning crater and discovered a Cosmic Warrior suffering from a strange techno virus with no memory of where he came from. Healing him in a mystic pool, Eldor inadvertently and unknowingly passed the warrior's techno infection to the entire magical planet. In gratitude for saving his life, the Warrior agreed to become Eldor's student and help free Eternia from the Snake Men. Until his memory was restored, Eldor dubbed him "Gray" in honor of Eternia’s brave king, and taught his apprentice to use a magic staff and the Book of Living Spells to defeat evil. Later Elder used the secrets of Transformation to cast the Three Towers into Sub-turnia awaiting a time of great Kings; when the past and future would need to intertwine! Eldor uses his magic as a member of King Grayskull's Masters of the Universe!
MOTU MVCreations #3: Comic Appearances:
MOTUC Mini-Comic Appearances: