Rex Origin and Meaning
The name Rex is a boy's name of Latin origin meaning "king".
Now that many dogs are named Max, it's safe to use this sleek, solid, regal name again for your child. And with the charm of its final x, its regal meaning, and its offbeat simplicity, Rex is definitely one to consider.
Coldplay's Will Champion used it for his twin son, and Natascha McElhone gave her little boy the doubly cool appellation Rex Coltrane, and Niki Taylor — intentionally or not — gave her son the full name of the British My Fair Lady star, Rex Harrison (who was actually christened Reginald). And quite fittingly, Rex is name of a toy T-Rex in Toy Story.
Other options: the French version Regis or the literal King.