André Castagnetas is the agen codenamed X-101. The codename "X-101" dates back to the early 1960s and is part of the Departement "X" (X Division) of the European Union with agents numbered X-101, X-102, etc. The X-101 codename was used by other agents before Castagnetas. X-101 works with a teenager named Squitt and a pet tiger, Sultan. His favorite cover is to pose as a gipsy, traveling along in a caravan. 

X-101 assisted Jean Sten against Wampus, and was present at Phenix's "funeral". He also fought Jaydee when he threatened Paris.