Mme Ralin reigns as the primary antagonist throughout the series, commanding a vast criminal network with significant influence across the Parisian underworld and beyond. Her organization operates as a powerful cartel, engaging in extensive illegal activities and controlling substantial underground operations during the 1920s setting.

She cultivates a sophisticated public persona, frequently appearing in high-society circles to project an image of wealth and legitimacy. This facade features elegant, fashionable clothing accented by distinctive accessories, notably wide-brimmed sunhats—most commonly a white hat with a violet ribbon—along with flashy jewelry and noticeable blue eyeshadow, contributing to her striking visual presence. Impeccable hair and makeup complete her carefully maintained appearance of refined authority despite her advanced age.

The character consistently crosses paths with the protagonists during their investigations, particularly as they pursue evidence linking her to criminal enterprises spanning multiple countries. Her operations extend beyond Paris to locations including Spain and America, where she interacts with historical figures of the era like Al Capone and Coco Chanel. These encounters occur during the protagonists' investigations into her activities aboard transportation such as the Orient Express and ocean liners, as well as at cultural landmarks like the Louvre and Opéra Garnier.

Her criminal influence persists throughout the series timeline, with references to historical events like the 1928 Olympics and Jack Dempsey's boxing career creating some chronological ambiguity regarding the exact duration of her operations. She appears variably as "Madame Lapin" in certain sources but remains consistently identified as the central antagonist figure. No substantive background information regarding her origins, personal history, or character development beyond her ongoing criminal activities and evasions of justice appears.