Handsome Dan is the bulldog mascot of Yale's football team.
Princeton had a tiger as a mascot and Harvard had the "Orange Man," a stand-in for Puritan John Harvard. So, in 1889, Yale undergraduate student Andrew Graves bought a bulldog and named him "Handsome Dan".
This is what the Hartford Courant had to say about it:
"In personal appearance, he seemed like a cross between an alligator and a horned frog, and he was called handsome by the metaphysicians under the law of compensation. The title came to him, he never sought it. He was always taken to games on a leash, and the Harvard football team for years owed its continued existence to the fact that the rope held." (Source)