If its a tek rex: Devestator

Dog

Because people name the dogs Rex

T-Rekt

REX BOX ONE

Shrex

Rexy buck tyrannus prime

Mr.T

My arms are bigger than carnos

Rexecutioner

Name it fluffy and go up to a random low level tribe and say do you wanna see my cute Dino it’s name is fluffy if the say yes call it and set it to kill them and say see cute

Captain Syret (Deadlands)

General Korvia! (Deadlands)

Grimlock

Bibby jr

Ares (Greek god of war)

Rexy (Jurassic world) : )

Pablo 🐧

Rex Ruthor

Devil Dinosaur (if red)

Rexy