A bulldog (right) with a dalmation.
A bulldog was a type of animal lifeform, a breed of dog native to the planet Earth.
History and specifics
In the year 2020, Alice Fontana owned a bulldog whom she named Gus. (TOS novel: The Rings of Time)
The bulldog was known stereotypically as a tenacious breed with intense focus. These qualities were presumably why Morgan Bateson was sometimes referred to as "Bulldog" as a nickname. (TNG novel: Ship of the Line)