Bulldog (noun)

1. A sturdy, medium-sized dog with a short, wrinkled face, a wide jaw, and a distinctive pushed-in nose.
2. A person who is obstinate, tenacious, or relentless in pursuing a goal or objective.

Origin:

middle english, from bull + dog.

Examples:

1. The bulldog is a popular breed of dog known for its loyalty and tenacity.
2. He was a real bulldog, never giving up until he achieved what he wanted.
3. The bulldog is a stubborn breed of dog.
4. She's a bulldog when it comes to getting things done.
5. You have to be a bulldog to get things done in this business.