Medusa's beauty was admired by all. Even Medusa. One evening she was invited to Athena's temple. Poseidon flirted with Medusa, which made the jealous Athena angry.
Athena change Medusa from a beautiful girl that any man would love to call their wife, to a hideous monster with snakes for hair.
Medusa soon realized that the hideous snakes came with a great power. As she fled from the temple, she came across a man who froze into stone when she saw him.
Word about Medusa and her snakes spread throughout the kingdom like a wildfire. Much like the news that the king was getting married. Perseus came to the King, begging him to not marry his mother. The King said he wouldn't if Perseus bring him Medusa's head.
While Perseus was thinking about how he could defeat Medusa, two gods appeared before him. It was Athena and Hermes. They told him to not look Medusa in the eyes but look at her through the shield that Athena gave him and then stab him with the knife that Hermes gave him.
When Perseus brought the king Medusa's head he was not happy. He thought that the assigned task was impossible and expected to see Perseus' dead body. Being a man of his word, he did not marry Perseus' mother.