Otus and Ephialtes are giant twin brothers, sons of Poseidon. They strive to push Jupiter (also known as Zeus) down from his kingdom.
Otus and Elphiates both wanted to prove superiority over the gods as they aggressively challenge the gods on several occasions.
They first threatened to pile Mount Bello on Mount Ossa. Enraged by their actions, Zeus was going to shoot them when Poseidon stopped him. They then tried to capture Artemis as she cunningly runs away and disappears.
The twins chased after her to her place. However, rather than finding Artemis, they saw a milk-white hind (a female deer). They both threw their javelins at the deer, but the deer disappears as well.
The weapons sped across the empty glade into the woods and hit the two giants instead as they both died in vain.
As the twin brothers died, Artemis thus enacts vengeance.