In "The Big Four", Agatha Christie gave him a mysterious "twin brother" named Achille
IN 1975 AN OKLAHOMA 
CITY LIBRARY WAS NAMED FOR THIS "INVISIBLE MAN" AUTHOR WHO WAS... [DOC] [TLE] The Agatha Christie Reader: August 2009 [PAR] Aug 3, 2009 ... We've had a hint of this before in The Seven Dials Mystery, but the idea ... Loathe 
him or loathe him, Mr Ellsworthy is a hint that this is Agatha .....