Monsters and mythical beasts
Not only did the ancient greeks believe in Olympian gods, but they did believe in terrible monsters and mystical beasts. Most of those creatures were siblings of gods or titans. The Gorgons, for example, were three bloodthirsty sisters. They were born by Gaia and the sea, had golden wings and snakes instead of hair. Only one of them, Medusa, was mortal and he who looks in her eyes turned into stone.

Lots of ancient greek monsters looked part human, part animal. Cyclops, for example, who crafted Zeus' thunderbolts, looked like huge men with only one eye. The centaurs were creatures with the torso of a man and the body of a horse. Some of them, like Chiron, were wise teachers, but most of them loved waging war. They were defeated with the help of Theseus.
The Calydonian Boar was one of the most furious beasts in the ancient greek myths, even though he looked like an ordinary boar. Most of the mythical beasts were hybrids of different animals. The fire-breathing chimera had two heads - of a lion and of a dragon and the body of a goat. She was slayed by the hero Bellerophon, who soothed another mythical creature - the winged steed Pegasus, using magical reins, given by the goddess Athena.