Miniature Giant Space Hamsters are primarily associated with Bioware's Baldur's Gate franchise. The Rashemen warrior Minsc supposedly befriends one by the name of Boo after sustaining a head injury. Though the veracity of this is often called into question, Minsc is unshaken in his belief that his friend and mentor Boo is a genuine Miniature Giant Space Hamster whose wisdom has aided him on numerous occasions. Little is known about the nature of these creatures, though if Minsc is to be believed, they are capable of speech and are quite intelligent.
Boo is a reference to the creature's from the Spelljammer AD&D campaign setting. In that setting giant space hamsters were discovered by the Tinker Gnomes who primarily live in the world of Krynn. They had several uses for the giant space hamsters ranging from livestock to a primitive power source for some of their space ships. The Animal Breeder's Guild created several variants of the Giant Space Hamster including a dwarf variant.
Space Hamsters make a reappearance in Mass Effect 2, also by Bioware. Though these hamsters are not confirmed to be of the Miniature Giant variety, when examined they will say the word "squeak" rather than actually squeaking, just as Boo does in Baldur's Gate.