There have been bad demons and there have been wicked demons but the one most infamous for his evil ways is probably the ten-headed Ravana. As mentioned earlier, Vishnu's doorkeepers Jay and Vijay had been cursed that they would be born as demons for three lives. Previously they were born as Hiranyaksha and Hiranyakashipu, and then as Ravana and Kumbhkarana.
In order to please Brahma, both the brothers and especially Ravana underwent severe austerities. For ten thousand years, he went without food. After every thousand years, he sacrificed one of his heads into the fire. At the end of the ten thousandth year, when he was about to sacrifice his last head, Lord Brahma appeared.
Ravana! What boon do you seek? asked Brahma.
Make me immortal! demanded Ravana.
It's not possible to grant a wish like this, explained Brahma. Ask for something else.
All right, then let me not be overcome in battle by either god or demon.
Brahma granted him his request and also restored the ten head
Ha! Ha! Ha! laughed Ravana. If gods and demons can't kill me then nobody can. I'm as good as immortal!
The conceited king never once thought that a man or an animal could be a threat to him. Armed with this boon, Ravana took possession of his stepbrother's kingdom Lanka.
Ravana then started troubling the various gods. He invaded the lower world and attacked Yama, the god of death. Poor Yama had to finally flee from there. He then attacked heaven and fought a long battle with Indra, the god of heavens. Ravana's son captured Indra and took him to Lanka. Henceforth Ravana's son came to be known as Indrajeet (the conqueror of Indra).
The entire universe was in terror of Ravana. The sun was scared to shine, the wind was scared to blow and the waves of the ocean were scared to move. Everything was in control of the wicked Ravana.
The gods were miserable and when they could take it no more, they appealed to Lord Vishnu for help. Well aware of Brahma's boon, Vishnu decided to take a human incarnation in order to put an end to Ravana.
In Ayodhya, there was a king named Dashratha, who was carrying out the Ashwamedha sacrifice in order to procure an heir for his throne. Lord Vishnu rose out of the sacrificial fire and offered a bowl of kheer (a sweet made from rice, milk and sugar) to the king.
Divide this kheer amongst your three queens and your wish will be fulfilled, said Vishnu.
Dashratha folded his hands in gratitude and accepted the divine gift. He gave half the contents to his senior queen Kaushalya. She gave birth to Rama. The other two queens received the rest. Sumitra gave birth to Lakshmana and Shatrughana. The third queen Kaikeya bore Bharata. The four princes grew up to be strong, brave and just.
Due to a certain situation, Rama, his wife Sita and Lakshmana had to leave their kingdom. While they were in exile, Ravana abducted Sita, and the two brothers went off in search of her.
It was not possible for Rama to overcome Ravana alone, so he took the help of bears and monkeys who had divine powers. Rama and Lakshmana, with their army of bears and monkeys, attacked Ravana's Lanka. Ravana and Kumbhkarana were both killed.
Rama's deeds of valour are described at length in the epic Ramayana.
In north India, the festival of Dussehra is very popular. It is celebrated to mark the victory of Rama over Ravana. But the brightest and gayest Hindu festival is no doubt Diwali, which is again related to Rama. On this day, Rama returned to his kingdom after fourteen years of exile and was crowned king. To welcome him, the people of Ayodhya illuminated the whole city.