A Boltzmann Brain is a type of intelligent being, usually defined as a Cosmic Entity of sorts, formed from mathematical or physical chaos rather than the normal organic processes which generally give rise to life. Although extremely unlikely, random changes in the quantum structure of a universe may give rise to a self-aware entity; this process never occurs in almost all universes, but in the infinitely large higher-level -verses it occurs infinitely often. Therefore, there are an infinite number of Boltzmann Brains in existence.
The bare minimum requirement for a Brain is that an entity is capable of self awareness, and as such, a Brain could be significantly less intelligent than a human. However, it is also possible that they are in fact immensely intelligent, having formed with a fully-developed neural system far more advanced than those of humans, deities, or some cosmic entities.