Rat King:
The original German term, Rattenkönig, was calqued into English as rat king, and into French as roi de rats. The term was not originally used in reference to actual rats, but for persons who lived off others. Konrad Gesner in Historia animalium (1551–58) stated: "Some would have it that the rat waxes mighty in its old age and is fed by its young: this is called the rat king." Martin Luther stated: "...finally, there is the Pope, the king of rats right at the top." Later, the term referred to a king sitting on a throne of knotted tails.

Medieval scholars have debated whether people may have been under the impression that the rat king was actually one animal with many bodies, with the “king” referring to the animal's aggregate size and weight. Legends have suggested that a “king rat” sat on the tails of the rat king, overseeing the movement of the animals as they attempted to navigate with their matted tails.

An alternative theory states that the name in French was rouet de rats (or a spinning wheel of rats, the knotted tails being wheel spokes), with the term transforming over time into roi de rats.