Answer:
The 12 main ones (called the Olympians) are:
Zeus/Jupiter
Poseidon/Neptune
Hades/Pluto
Hera/Juno
Demeter/Ceres
Hestia/Vesta
Ares/Mars
Apollo
Artemis/Diana
Aphrodite/Venus
Hermes/Mercury
Athena/Miverva
(Greek names are given first, Roman second)