Paracelsus made one remark about water spirits that outran everything else he wrote on the subject. Lacking souls of their own, he said, they could acquire one by marrying a man, and the marriage bound the man in turn. He offered it as a piece of natural philosophy. It became the plot of a whole century of European art.
Friedrich de la Motte Fouque's novella Undine, published in 1811, is the point at which the remark turned into a story. A water maiden marries a knight, gains a soul and with it the capacity to suffer, and is betrayed. The book was an immediate and lasting success across German Romanticism and it fixed the shape that every later version would use.
What followed is a small industry. E. T. A. Hoffmann set it as an opera, Albert Lortzing set it again, and Tchaikovsky wrote an Undina he later destroyed most of. Jean Giraudoux's play Ondine reached the Paris stage in 1939 and has been revived steadily since. Hans Christian Andersen's Little Mermaid belongs to the same family of stories about a water being who trades her element for a soul and a man, and loses both.
The strangest survival is medical. Congenital central hypoventilation syndrome, in which the automatic control of breathing during sleep fails, was for many years called Ondine's curse, after the version of the tale in which the betrayed water spirit condemns her husband to keep breathing only so long as he remembers to. Clinicians have largely dropped the name, but it is still met in older literature, and it is an unusually direct route from a sixteenth century marginal note to a diagnostic term.