Medusa was one of three gorgons that arrived on Earth during Humanity's early history.
She was the better known of the three and was often depicted as being a beautiful women with snakes for hair (though this was dramatized). Like all gorgons, she was noted for having the power to turn anyone who looked at her to stone. In a challenge, she was killed by the Greek hero Perseus.
The Doctor and Zoe encountered Medusa in the Land of Fiction.