The Cat Lord first appeared in the first edition Monster Manual II (1983).
The Cat Lord, Hawk Lord, and Wolf Lord appeared in second edition under the "Animal Lord" heading in the Monstrous Compendium Volume Outer Planes Appendix (1991). The Cat Lord, Hawk Lord, Lizard Lord, and Wolf Lord appeared in second edition for the Planescape setting under the "Animal Lord" heading in the first Planescape Monstrous Compendium Appendix (1994).
In the game, each animal lord is a humanoid being, powerful like a celestial paragon or demon prince, that represents all animals of its chosen type. For example, there is a Mouse Lord, a Lizard Lord, and a Hawk Lord. The most well-known animal lord is Rexfelis, the Cat Lord.