Who is Yuvanov from The Case of Comrade Tulayev and what is their importance?

Yuvanov is a Bulgarian who is working for the Russians in Spain. He is young, strong, and square and has an animally hostile face. His wavy, black hair is slicked back with pomade and his mustache is neatly trimmed. He would remind one of a lion tamer. Yuvanov has a discreet voice and velvety eyes that are unpleasant. He is responsible for creating false charges against Stefan Stern.