Basic Information
In the Cthulhu Mythos, a group of beings often mistaken for gods by less powerful races (such as humanity). The Great Old Ones are a poorly defined group (as is perhaps natural for entities largely beyond human comprehension) and highly variable, seeming to share few traits beyond colossal age (generally they at least predate life on Earth; many predate the current universe entirely — definite Time Abyss), frightening power, horrifically alien nature (damaging to human sanity), and general Eldritch Abomination-hood.
Some authors - including HPL himself at times - seem to grant Great Old Ones some degree of divine power, including the ability to provide power investiture to their followers. The line separating them from the Outer Gods is not at all clear.
Some authors (e.g. August Derleth and Brian Lumley) make the Great Old Ones a somewhat more coherent group, and enemies of the Elder Gods.
Some Great Old Ones include: