Read if you know a lot about Greek mythology!?

Alright I have a project due Friday, I know I'm starting late but I have a few questions. Who were the 12 Olympian Gods? I'm looking it up and some say Zeus, Hera, Hades, Poseidon, Hestia, Athena, Artemis, Apollo, Aphrodite, Ares, Hermes, and Hephaestus. And others will have Demeter instead of Hades, some will have this God whose name begins with a D, I don't remember it's like Dyphulus or something like that, instead of Hestia. I'm so confused, please help!