In the 5th chapter of Devi Mahatmay, there is a story of Sumbha and Nisumbha
They were Demons (Rakshasa) who performed enormous penance to conquer 3 worlds. There penance was on Pushkara, a religious place in India. They performed penance for 10,000 years and were finally given a boon.
Now somehow Sumbha heard the name of Parvati and how beautiful she was. He decided he wanted to marry her. Of course she refused.
First he sent Dumralochana one of his top aides. He went there with an army of 60,000 soldiers. Parvati killed all of them in a trice. Then sent Chanda and munda. Once again, Parvati in the form of Durga killed both of them. Finally he sent Raktabeeja. Now this demon had a boon. From drop of blood that would fall from his body, when it falls on the ground, another demon just like him would appear. So Kali (Durga) killed him by drinking every drop of blood that came from his body, without letting if fall on the ground.
This story, is the story of liberation, giving step by step levels that have to be conquered.