Moebius

His series The Airtight Garage is the most epic surrealist graphic novel I have ever encountered.

And of course, he was involved in the tragically canceled Jodorowsky production of Dune, along with Giger and Dan O'Bannon. (Details here.)

Some of Jodorowsky's concepts related to Dune eventually resurfaced as the graphic novels The Incal (with art by Moebius) and The Metabarons (with art by Juan Gimenez).