As the legend says, Kumbhakarna was the younger brother of Ravana. He is said to be huge, intelligent and good at heart. He even tried to warn Ravana what he was doing was wrong. This is how Kumbhakarna ended up having to sleep for six months. Kumbhakaran was intelligent and powerful, he felt that instead of Deity Indra he should be the one to sit on the throne of Indraasan.
The three brothers Ravana, Kumbhakarna and Vibhishana performed yagna to please the Lord Brahma. It is said that Indra was scared of losing his throne so he already had made a prior request to Devi Saraswati to make Kumbhakarna say ‘NidrAsatongue and ‘IndrAsana’.
Lord Brahma appeared in front of them and asked them what they wanted. When Kumbhakarna’s turn came, Devi Saraswati sat on his tongue and he asked for ‘Nidrasana’ which is a sleeping bed instead of ‘Indrasana’, which is the throne of Indra. Kumbhakaran was shocked at what he said. He tried to amend his mistake. However, it was too late. By the time, Kumbhakarna realized his mistake, Lord Brahma already had said ‘tathasthu’. This meant the boon was granted.
Kumbhakarna who didn’t want this fault to cost him his boon even asked Brahma not to consider his wish. But, Brahma told him that there was no way to undo the grant. Hence, Kumbhakarna was granted a sleeping bed from the Lord Brahma, it is said that, Kumbhakarna used to sleep for 6 months and stay awake for the next 6 months to eat whatever he could find to make sure his hunger is fed for the next six months.