H.P. Lovecraft creates the character in his short story "The Call of Cthulhu," published in 1928. The related mythologic universe created around Cthulhu is called the Cthulhu Mythos. Because Cthulhu Mythos communicates through people's dreams, it is also believed connecting with the world's collective subconsciousness.
There is a lot to talk about Cthulhu because he is not good nor evil. He is powerful yet full of unknowns. You can even find toys in his character at Amazon, which you can use as a prop when talking about it.