Madrox the Multiple Man started as kind of a joke, as the villain in Giant-Size Fantastic Four #4.
Why did a regular future member of several X-teams get his debut in an issue of Fantastic Four? Why, because Len and Chris wrote the issue!
Fortunately, Peter David got the character into X-Factor and turned him into a noir-ish fellow tormented by his own fracturing psyche. Madrox, when written by David, is probably one of the most complex and intricately developed characters in the Marvel Universe.
Fun fact: According to the great CBSBG site, he started out as “Zerrox the Multiple Man” before Xerox threatened litigation.
Title: “Madrox the Multiple Man!”
Credits:Chris Claremont (co-writer), Len Wein (co-writer/editor) ,John Buscema, Chic Stone and Joe Sinnott (illustrators)