This is a tough one because, going on Choas' first hint, there are any number of characters that can be the answer:
Albus sent Hargrid after the stone at the start, the teacher with the turban was trying to help Voldermort get it and Harry, Ron and jailbait all tried to get the stone to stop Voldermort getting it. And all of the characters were introduced in the first book.
This is troublesome. If Choas' had hinted that the original owner is the name than that'd be different. I'm going with Hagrid myself.