@ZelosseFollowing, and there's a few differences. Kaathe is an actual trained warrior, and uses his magic to fight. The character I'm thinking of only knows how to perform, and doesn't quite know how to do anything more than mislead, and wound.
Kaathe is a dark person that figures Fate only wants to ensure that everyone is thrown under the wagon. The student is more cheerful, and wants to see a world of joy and whatnot.
Aside from that, you're correct about the reason I'd probably have them arrive. To follow their mentor, and receive a better understanding of Illusory magic.