There are three dog-type units featured in Age of Empires III: War Dogs and the Explorer Dog. The third, Fluffy, is only available via cheats.
“
War Dog. A fierce canine that obeys commands.
”
—In-game description
The War Dog is unique to the Spanish and can be trained by the Explorer. The Spanish start a random map game with one War Dog alongside their Explorer, and can train up to four more.
War Dogs can also be rescued at some treasure sites.
The Spanish Conquistadors brought dogs with them to the New World. These were big, fierce dogs, probably a mix of mastiff and greyhound. They were good at tracking, hunting, and killing prey (often human). Becerrillo, which means "little bull calf," was owned by Spanish Conquistador Ponce de Leon. Becerrillo sired the more famous Leoncico, "little lion," who stowed away in a wooden cask with his owner, the Explorer Vasco Nunez de Balboa.
”
—In-game history
“
Explorer Dog. Your Explorer's loyal companion.
”
—In-game description
The Explorer Dog is available to European civilizations other than the Spanish and, like the Explorer, cannot die when its hit points reach 0. Instead, it collapses and must be rescued when an allied unit or building is near and it has enough hit points, or ransomed.
The Dog was originally cut from the original Age of Mythology, however it was meant to return as a trainable unit for the Chinese, likely as a scout, before becoming just a Scenario Editor unit, similar to the Cataphract.
When the Explorer Dog collapses, a text box appears near it that quotes Hamlet's final line from the Shakespearean play Hamlet: "Horatio, I am dead; Thou livest; report me and my cause aright To the unsatisfied."
Although the War Dog/Explorer Dog unit portrait shows a German Shepherd dog, the two in-game variants resemble an Belgian Shepherd Malinois and a English Mastiff.