Ivan

In the short story The Chess Problem (later chapter 11 of The Big Four), Ivan is the manservant of the chess master Dr Savaronoff. According to Captain Hastings, Ivan had a peculiarly wooden face. "It seemed impossible to believe that the impassive countenance could ever display emotion." For a while, Poirot suspected that Ivan was Number Four in disguise and possibly the murderer of Gilmour Wilson but it later turned out that he was entirely innocent.