What does the expression green eyed monster mean?

If someone calls you a "green eyed monster" they are saying you are jealous. It's similar to the expression, "green with envy". Some people say this phrase comes from the Marvel Comic Book character, The Incredible Hulk, but it most likely originated from Shakespeare as he referred to "green eyed jealousy" in his play, The Merchant Of Venice; as well as "the green eyed monster" in Othello.