A mimir is a magical construct that serves as a living encyclopedia. They are typically made of a silvery metal and often take the form of a disembodied head. Morte pretends to be one of these, but possesses his own free will and is not made of metal. If pressed on the issue, he will admit to the Nameless One that he is not, in fact, a mimir.
In Norse mythology, Mimir is a wisdom deity. Mimir owned a magical well which bestowed knowledge upon any who drank of its waters. He himself drank from the well, and it made him wise. After being beheaded later in life, his wisdom was magically preserved in his disembodied head so he could serve as Odin's advisor and counselor.