Nah. Cthulhu was invented by H.P. Lovecraft. (So was the Necronomicon, despite what some teenage Satanists will tell you.)
There are people who insist that he was based off of Kutu, a Sumerian or Babylonian god. That's not really true either since there is no such god in any Middle Eastern mythology... that we know of. There were plenty Mesopotamian sea gods like Tiamat, Yam-Nahar, Lotan, Behemoth, Rahab and Leviathan, but aside from being evil, they don't share much in common with Lovecraft's creation. (Number one being that said sea gods always end up getting PWNED by Marduk, Baal, Hadad, Yahweh, etc.)
According to the Assyro-Babylonian Mythology FAQ, the closest the researcher can find to Cthulhu is Kutha, the patron city of Nergal, the god of the underworld. But Nergal wasn't really ever cast as pure evil, nor was he depicted as a giant squid. Dammit.