"He's Yorath, a shape-shifter so old he can't keep his own shape. He needs to borrow from other beings."
Yorath Yewbeam (b.1850) is a shapeshifter and a major antagonist in the series. He married Vera Kuragina, a hypnotist, and had two children, Manley and Yolanda Yewbeam. Yolanda was Yorath's favorite, and she inherited his castle at age twenty-one.
Paton Yewbeam encounters Yorath in Yewbeam Castle when he goes there to stop Yolanda from coming to the city. Yorath attacks Paton and feeds from him for a week until Paton finally escapes. As Paton leaves Yorath calls out, 'If you harm my dear one you'll pay with your life.' After Paton kills Yolanda, Yorath swears vengeance on him and it is for this purpose that he goes to Bloor's Academy and poses as a teacher there. To pass as a teacher, Yorath imprisons Tantalus Wright, Vincent Ebony, and Mr Pilgrim in Yewbeam Castle and 'borrows' their personalities and shapes. In this composite body he is called 'Tantalus Ebony'.
When Yorath hears that Paton has gone to the Castle of Mirrors he follows him, intending to have his revenge on Paton for killing Yolanda. He charges at Paton, but Christopher Crowquill, Billy's guardian, sacrifices himself to save Paton Yewbeam by dragging himself and Yorath over the edge of the cliff. Yorath's death is uncertain, but he most likely died because two of the people he kept captive said they awoke suddenly from their semi-conscious state and found they could move again.
It is stated in the third and fourth books that Yorath is so old that he has no form of his own and must borrow the forms of others. The people whose forms he takes become trapped in a state of semi-consciousness and suspended animation in which they cannot move or speak but don't need to eat or drink.