Who is Stivo from Plain Kate and what is their importance?

Stivo is Behjet's twin brother, Daj's son, and Drina's father. He warns Plain Kate not to cause trouble for Drina, thus, when Drina is attacked while acting on Plain Kate's behalf, he is the first to turn on her. When Stivo learns that Taggle can talk, he becomes even more convinced of Plain Kate's evil.