Klingon monster dog

Klingon monster dogs were a type of lizard-dog kept as pets by Klingons.

Commander Kruge kept a ferocious monster dog as a pet aboard his Bird-of-Prey. It died when a torpedo hit the ship. 

Background
The term "monster dog" is not the "official name" of this animal, however, it is consistently used by visual effects supervisor Ken Ralston during an interview in the Star Trek III: The Search for Spock Special Edition DVD, which discusses the creation of the puppet. According to magazine articles at the time of the release of the movie itself and, later, the DVD SE's text commentary by Denise and Mike Okuda, some of the members of the puppetry team dubbed it "Fifi Rebozo."

According to the script, the "monster dog" was referred to as "the Beast," and described as "a half timber wolf, half lizard."

Apocrypha
In the novelization of Star Trek III, the creature was named "Warrigul."

In the Universal Studios Hollywood theme park's Star Trek Adventure experience, a child participant would be selected to play a similar Klingon pet in each presentation. In the closing credits of the edited "episode," this juvenile creature was called a "puppy lizard."