The Great Old One, or High preist of the Great Old Ones depending on the story you read.
Less a god than a monstrous horror resembling an octopus, man, and dragon cojoined from a creation wholy unlike birth.
Best pronounced sucking water into your lungs whilst beining dragged down by a tentical.
Anyone shewn Cthulhu, sometimes even in representations fearfully crafted by his cults, cannot survive sane.
"Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn" In his city, R'lyeh, Great Cthulhu waits, dreaming.