The way I have it, The Outer Beings came to be at about the same time as the
Old Ones, but they are less powerful. A single Outer Being is more than a match
for an Immortal - even a Hierarch - but they are "safely" imprisoned
away where they cannot do any harm - for now. A group of Immortals could take on
an Outer Being, though it would be a tough fight.
Among the known Outer Beings:
Akh'All the Unmentionable (think of a mass of writhing tentacles crossed with a
giant festering slug) - Greater Outer Being
He-Who-Must-Not-Be-Seen (a black pit of nothingness, containing...a hideous
monstrosity whose appearance is so hideous even Immortals would be driven
insane) - Greater Outer Being
Rasthz the Many-Mouthed (a giant beholder-like creature with hundreds of mouths
instead of eyes) - Greater Outer Being
Rosheg-Kha (a 10' tall creature resembling a lizard man, but covered in
festering sores and bubbling pseudopods) - Lesser Outer Being
H'rug (a spindly collection of bony tentacles, pseudopods, eyestalks, and
brain-like lumps, measuring about 2 miles long) - Lesser Outer Being
Feel free to add more, or detail any of these guys.