Both designers were born in 1968–Slimane in Paris, France and Simons in Neerpelt, Belgium. Neither has a degree in fashion design.
Slimane pursued both fashion design and photography at a young age, but went to school for Art History at the Ecole du Louvre. After four years designing menswear for Yves Saint Laurent (where he was hired by Pierre Bergé), he left to become creative director at Dior Homme in 2000, where his designs earned him a CFDA for International Design–the first ever given for menswear. He left Dior Homme in 2007 and has been pursuing a photography career in Los Angeles up until his appointment at YSL in March.
Simons interned with Walter Van Beirendonck and studied industrial design and furniture design. He launched an eponymous menswear line in 1995 which he presents in Paris, but designs from Antwerp, Belgium. Like Slimane, he quit fashion for a bit in 2000 due to feeling constrained by its business side, but relaunched in 2001 after a new deal with a different manufacturer. In 2005, he launched a diffusion menswear line, Raf, and was appointed creative director at Jil Sander–a position he held until this February, when he was ousted so that Sander could return to her eponymous label. He was appointed creative director at Dior in April.