For more mature French comics, Mobius and Jodorowsky dominate the conversation but I’ve been blown away by Philippe Druillet. As this review of Loan Sloane says:

In terms of sheer conceptual imagination when it comes to heroic science fiction in comics, Philippe Druillet is perhaps the only creator who approaches Jack Kirby’s creativity.

Also worth checking out Métal Hurlant and the output of its publisher Humanoids.

There are good English translations of them all available.