Poseidon did because Perseus was going to kill Medusa which Poseidon fell in love with before she was turned into a monster by Athena when Poseidon made love with Medusa in Athena's temple and that was very rude because Athena is a virgin.Actually Poseidon did not send out a sea monster to kill him a girl name Andromedea got chained to a rock and the sea monster was out to kill her and Perseus saved her by slaying the sea monster, and in the end they got married to each other.
Perseus killed the Gorgon Medusa and the sea monster that was about to devour the beautiful Andromeda.
To save Andromeda, the princess he had fallen in love with.
Perseus killed the Gorgon Medusa and the sea monster that was about to devour the beautiful Andromeda.
Perseus only loved and married a woman named Andromeda. He won the right to marry her after he slew the sea monster and freed her from where she was chained - she was to be an offering to a sea monster, sent by Poseidon
He kills the sea monster. It was sent by Poseidon to swallow Andromeda for a sacrifice to him. Perseus killed it and saved her by driving his sword in its mouth. He also by accident killed Acrisius, his father-in-law.
Perseus kills Medusa, by cutting off her head, and the sea monster, by turning it to stone, using medusa's head.
Perseus, son of Zeus (The Perseus, not Percy Jackson) he used Medusa's head to petrify the Kraken so it wouldn't kill her as a sacrifice.
Medusa and a ketos, which is a huge sea serpent. he turned it stone with Medusa head to save the princess Andromeda
medusa and the sea monster
Perseus unchained Andromeda from her rock, and slayed the terrible sea monster.
After he gets the agreement of her parents to marry Andromeda, Perseus saves her from the sea monster.
Andromeda was rescued from Perseus.