Who is Yuri from Taltos: Lives of the Mayfair Witches and what is their importance?

Yuri is a member of the Order of the Talmasca. He runs into Samuel after being attacked and injured by a hired assassin. Samuel takes care of Yuri, an act that serves to bring Yuri and Ash together. Yuri can't believe that members of the Talmasca were involved in the attack and arranges to meet Stuart Gordon.... someone he sees as incorruptible. Sadly, he realizes Stuart had a role in the plot after learning that he has a Taltos female captive in his possession.