The Elder Stain
External Intelligences, or E.I.’s, are what the mediaeval magic types called demons, gods, spirits, what have you. Sentient aliens, basically, from the those cosmological domains where the the anthropic principle predominates and some sort of sapient creatures have evolved. Some of them are strongly superhuman, others are dumb as a stump from our perspective.
The Elder Gods are those Gods who have established themselves in our paradigm and who are often worshipped as behign and adored. They are enemies of the Outer Gods and their servants, sometimes appearing to be on the side of man in the face of a shared enemy.
The Outer Gods are vastly more powerful than the entities trapped on earth and function on a cosmic scale, and are free to roam the multiverse. Many are too mad or too inhuman to effect our sphere directly and it is only through the vast scope of their worshippers that we know of them at all.
Great Old Ones
The Old ones are not as powerful as the Outer Gods, nor do they have as much influence. Nonetheless, they are served by devoted congregations of worshippers, made up of both human and non-human cults. They live or are trapped, for the most part, within the earth sphere.