The Marquis de Sainte-Croix was the proprietor of the Long Rooms. He was short and plump, but elegant. He dressed in the height of fashion, save for his hair, which he wore long, tied back, and powdered in the style of the previous generation. This contrast made his age hard to guess. A French immigrant, the Marquis spoke excellent English.

During Horatio Hornblower's unemployment during the Peace of Amiens, it was the Marquis that hired Hornblower to play whist with any three that needed a fourth.