Dogmeat

Dogmeat is a dog living in the Commonwealth in 2287 and a possible companion to the Sole Survivor. He will be named Dog until the Sole Survivor speaks to Mama Murphy about his true name during the quest When Freedom Calls, or until Nick Valentine reveals his name during Getting a Clue, when Dogmeat has to sniff out Kellogg.
Background A typical Commonwealth canine, Dogmeat is capable of tracking a man's scent for miles, an example is when he must track Kellogg in Getting a Clue. While he doesn't really have an owner, he is a loyal and faithful companion to those he accompanies, according to Mama Murphy when the Sole Survivor speaks to her in the Museum of Freedom in Concord, she states that Dogmeat "is his own man."
During the time that the Sole Survivor was cryogenically frozen in Vault 111, Dogmeat assisted Nick Valentine on a number of cases, and also accompanied Preston Garvey and his group of settlers on their way to Concord.
When the Survivor arrives, they can choose to adopt Dogmeat, who will accompany them on their travels throughout the Commonwealth. Dogmeat's remarkable senses and tracking abilities come into good use when the Sole Survivor searches for Kellogg.