Medusa

Medusa was one of three Gorgons which plagued Ancient Greece during humanity's early history. The best-known of the three, she was slain by Perseus.

Origins
According to one account, Gorgons were alien beings from the planet Gorgos. Three, including Medusa, came to Earth during humanity's early history. Their true form was the mass of snakes usually described as their "hair", who possessed human hosts. (TV: Eye of the Gorgon)

According to another account, however, Medusa was originally a human woman who was very proud of her beautiful hair. She gave offence to an Immortal, Athene, who transformed her into a hideous Gorgon — a woman with a face that turned everyone she looked at to stone, and snakes for hair — as punishment. (PROSE: Mythical Monsters)

Death
Medusa was killed by the Greek hero Perseus, (TV: Eye of the Gorgon) who avoided being petrified by never looking at Medusa directly, instead using his shield as a mirror. He beheaded her. Her blood had supernatural capabilities; a winged horse, Pegasus, sprang from it, and the blood which trickled from her left side was a powerful poison while the blood which trickled from her right side could raise the dead. (PROSE: Mythical Monsters)

Legacy
Medusa passed into legend. (TV: Eye of the Gorgon, PROSE: Mythical Monsters) Thorsuun's smile was thought by Martin Kerbe to be the kind which he "used to read about in stories of the Medusa turning her victims to stone". (PROSE: Invasion of the Cat-People)

The Second Doctor and Zoe encountered Medusa in the Land of Fiction. This was a fictional construct based on the legends surrounding the real Medusa. (TV: The Mind Robber)

Logan compared the Cyrene's appearance to a Medusa. (AUDIO: Bang-Bang-a-Boom!)

A woman resembling Medusa was one of the attractions at the Ancient Worlds theme park on Dewyn. She came under the control of a Chiffala and was used to attack guests attending the park. (COMIC: Minor Trouble / Inhuman Sacrifice / Crimes and Punishment)

Alternate timelines
In Andrea Yates' World, where the Trickster manipulated events so that Sarah Jane Smith died in 1964, the Gorgons never came to Earth. As the Trickster explained to Sarah Jane while she was in limbo, he had turned away all the foes she would have defeated, his intention being for her absence to allow Earth to be destroyed by the meteorite K67. (TV: Whatever Happened to Sarah Jane?)

Behind the scenes
Medusa was played by Jemima Rooper in the BBC series Atlantis.