Belgian-born Mulier studied architecture at the Brussels Institut Saint-Luc, and was subsequently invited by Simons to do an internship at his namesake label, before returning in 2002 as senior head designer to lead the creative team.
He followed Simons to Jil Sander in 2006, where he became the director of accessories. In 2012, when his mentor invited him to join Dior, Mulier jumped at the chance to work in an atelier of one of the original Parisian couture houses, assisting Simons as the link between the designer and the studio staff.
His role at Dior was highlighted in Frédéric Tcheng’s documentary “Dior and I,” which revealed Mulier as the middleman between the Simons and the atelier.
When Simons moved to lead Calvin Klein after three years at Dior, Mulier was appointed creative director, charged with managing the design teams. The debut collection for the Autumn/Winter 2017 season received critical acclaim — Mulier took a bow with Simons at the end of the show.