On Thursday, after the markets closed here, Hermès International said Dumas, 67, would relinquish his functions of artistic director and chief executive officer, effective in January.
Hermès cited only "personal reasons" for the decision, but Dumas' increasingly frail appearance and reduced public profile suggest his health has been declining.
Patrick Thomas, 58, an Hermès veteran who rejoined the firm in 2003 and was named co-ceo last year, will take sole control of the management helm.
"[Dumas] was a giant. When I was told I would succeed the giant, I felt very small," Thomas told WWD. "He has a fantastic, creative mind…and he is known as an outstanding businessman. He's a poet and a grocer at the same time."
While the announcement seemed sudden, Thomas said preparations for Dumas' retirement were quietly set in motion several years ago and health reasons did not precipitate Thursday's bombshell.
"There is nothing new in his health which would justify this change," Thomas said. "He is still active in the company, although less so than before. He's gradually reducing his involvement."
Dumas — who effortlessly imbued disparate product categories with the soigné but lighthearted Hermès spirit — will be succeeded as artistic director by his son, Pierre-Alexis Dumas, and his niece, Pascale Mussard, 48, as joint artistic director.
The younger Dumas, 39, was named deputy artistic director in 2002 after leading Hermès subsidiaries in Great Britain and, before that, Hong Kong.
Mussard, a 25-year veteran of the company, rose through the ranks of press attaché to direct advertising and communications departments and then window display. As part of behind-the-scenes efforts to prepare for Dumas' eventual departure, she was also named an artistic deputy in 2002.
Dumas senior was not available for further comment. Yet in a statement reminiscent of his quirky yet heartfelt Hermès initiatives like the "Year of the Hand" and the company's heavy sponsorship of the arts, he said, "It is with the utmost confidence, and with the unanimous approval of the board that I will hand over the reins of our family house to Patrick [Thomas] and to the executive committee which works with him. From the roots of Hermès, they will know how to draw the sap for the new branches that will grow in response to the dreams of our client."