What is "fantomex"

Fantomex is a fictional superhero appearing in American comic books published by Marvel Comics. The character is commonly associated with the X-Men titles. Fantomex first appeared in New X-Men #128 (August, 2002) and was created by Grant Morrison and Igor Kordey. Initially introduced as a character similar to Fantômas and Diabolik, he is later revealed to be an escaped experiment from the Weapon Plus Program.