Blueberry came first and he signed his art "Gir."  When he started doing the science fiction/fantasy stuff, he adopted the new name, Moebius, to differentiate it from his other work.  The series actually grew out of an earlier series, Fort Navajo, which began in 1963.  It was supposed to be an ensemble feature; but, Blueberry quickly became the star.  The stuff that Marvel reprinted was from the 70s; but, the feature was a hit, in the 60s.

Giraud was a fan of earlier European western comics, like Frank et Jeremie, and had worked with mentor Jije, on his Jerry Spring, in Spirou.  Giraud had talked to writer Jean-Michel Charlier about doing some western comics; but, he wasn't interested, at the time.  It was after he was sent by Pilote to the Mojave Desert, to gather material for some of their educational comics, that the idea of the landscape and a western came to mind.  he approached Jije about doing it, but he felt it was a conflict of interest, since he worked for Spirou, which competed with Pilote, but recommended Giraud.  Thus was born Fort Navajo, soon to be retitled Blueberry.

Amazingly, we have only seen one film realized out of it, and not a particularly good one or even a remotely faithful one, with the 2004 film, starring Vincent Cassel.  There was an attempt to finance a tv mini-series, for European television, in 1983, with Sergio Leonne expressing interest, which failed to draw investors.  A few years later, Martin Kove (Kreese of Karate Kid fame and the tv show Cagney and Lacey), was involved in an attempt to do a movie.  Kove wanted to adapt the comics; but, the producers wanted to turn it into a generic western.  It didn't go anywhere.  Another production was attempted, which turned it into an Indiana Jones ripoff, with Aztec pyramids and lost treasure, which thankfully went nowhere.