How do you get Hercules on poptropica's mythology island?

Hercules is not going to help you during the hunt for the Five Sacred Items. It is only after Zeus has taken them from youthat he agrees.

Get the 5 sacred items and return them to Athena at the Tree of Immortality. You will also need the teleporting Mirror from Aphrodite, on the beach in Poseidon's realm.

His contribution is to move the large rocks blocking you from the Hades and Poseidon throne rooms, and to smash the lock on the Mount Olympus gate. In Olympus, he finds a snake which is actually Medusa, who turns him into stone then disappears.