Rex

Rex comes from Latin, meaning simply "king" — the word itself, not a title derived from it, but the root from which all the related words branch. It is the most direct possible royal name in the Latin tradition: one syllable, absolute authority, no metaphor required. As a companion name, Rex declares the same thing with the same economy: this animal is the monarch of this household.

Rex holds the #87 spot among US pet names, with over 1,130 companions sharing it. The name has a long and distinguished history in pet naming — it may be the oldest continuously popular companion name in the Western tradition. Rex suits companions with a natural authority, those who occupy space with confidence and receive attention as their due. The name is particularly associated with larger, more imposing companions, but its crisp single syllable gives it an appeal that transcends size.