Zagor was a being who trained Gary Seven, and probably was the one who sent him to Earth. He was not Human, but he took on the countenance of an old man when he dealt with Seven or any other Human. That way no operative could ever reveal who had sent them.

Zagor warned Seven to keep an eye on young Khan Noonien Singh and others like him, as well as detect any attempts to interfere with the timeline. (TOS - Strange New Worlds 10 short story: "Time Line")

While he does describe his people, it would seem that he was a member of the Aegis, even though his race was not stated. It is also possible that he could have been from another race who was in the same position as Gary Seven, working for the Aegis.