According to ThoughtCo., bain-marie got its name from Maria the Prophetess, also known as Mary the Jewess. She is said to have lived between the first and third centuries and is believed to be the first known Western alchemist. Though none of her writings remain, she is often cited by the fourth-century alchemist Zosimos of Panopolis, and she is universally credited with the inventions of the bain-marie and several other alchemical processes and equipment, including the distillation apparatus known as a tribikos, per Chemistry World. According to SciHi Blog, some consider the tribikos to be a prototype for the modern-day pressure cooker.
As for the bain-marie, this heated bath named after its inventor is an invaluable tool in cooking. As MasterClass explains, a bain-marie — which involves placing a smaller container (with ingredients) over or inside a larger container containing hot water — allows for the creation of sauces like hollandaise, tempered chocolate, and according to Cook’s Illustrated, perfectly smooth custard. As Mary the Jewess must have used in her alchemical experiments, the heated water bath serves as a double-boiler, one that gently heats items like chocolate or custard at a controlled temperature (via Wasserstrom).