He's The Keeper of all Secrets (and as such a bit less idiotic and blind than Azathoth and less crazy than Nyarl). Also he's a cool guy once you get past the nth sphere...
Tastes good.
I meet it once, I was inna bar and he came for a drink, so we began talking and he was so fun, with really old stories, and when I told him that I had to go cuz it was like 3 a.m. and my GF will kill me he not only stopped and move us backward in time, but keep paying for the rest of the drinks and telling me stories about the cool parties at Hastur's place, how Abhoth speaks BS when drunk and the "always crying for good ol earth" Ubbo-Sathla...It's really a nice deity to talk to.
Not only is he a evil elder being with control of time and space, but he is also an absentee parent.
Yog Sothoth—He is one—He is all—All are He. He is the Opener of the
Gate, and the Gate itself. All who wish to know the secrets of the Universe must pass
through Him.....
He is fairly easy to summon and can mate with humans and who knows what else. Yog-Sothoth is also the gate, the key and the guardian of the gate. Past, present, and future, are all one in Yog-Sothoth and he knows where all the old ones did and will break through. Sure beats Y'Golonac who just can stomp around and bite people with his hands (and only if they have read Revelations of Glaaki) or Azathoth or sits around all day listening to bad music at the center of the universe.
I would put Nyarlathotep at a close second, however...
Yog-Sothoth is apparently an omnipotent/possibly sane version of Azathoth. It's dominion is of a greater reach than the Old One's, I think in fact it may be able to control the travel within time and space.
i.e. from The Dunwich Horror—
“Yog-Sothoth knows the gate. Yog-Sothoth is the gate. Yog-Sothoth is the key and the guardian to the gate. Past, present, and future are one in Yog-Sothoth.”