Kumbhakarna
Jaya and Vijaya
Jaya and Vijaya are the two gate-keepers (dwaara-paalakas) of Vaikunta, the abode of Vishnu. They are similar to Vishnu in that they have four arms, bear a conch, discus and mace and are blue-hued. The Bhagw*atha tells the story of the four maanasa putras of Bramha, Sanaka, Sanandana, Sanaatana and Sanatkumara, collectively known as the Kumaras, who are yogis but whose physical appearance is that of little children. When Jaya and Vijaya taking the Kumaras lightly forbade them from entering Vaikunta, they (the Kumaras) wanted to rid the gate-keepers off their obscurity and cursed them to be born on the earth. When Jaya and Vijaya begged Vishnu to waive the curse, Vishnu partially obliged them by giving them two options. They could either be born seven times as his devotees or three times as his adversaries, who would be killed by Vishnu himself.
In order to reduce the duration of their separation from their beloved lord, they chose the latter. Thus were born Hiranyaaksha and Hiranyakashipu, Raavana and Kumbhakarna, and Shishupala and Dantavakra.
Prayer gone wrong
Raavana and Kumbhakarna were brothers born in Treta yuga. Kumbhakarna was Vijaya reborn, to be killed by the avataara of Vishnu as Raama. Like Raavana, Kumbhakarna also possessed many virtues, such as piety, fearlessness, loyalty, and affection.
He had two sons called Kumbha and Nikumbha. When Kumbhakarna performed severe penance and invoked Bramha, Indra, fearing that he may ask for his throne, requested Saraswathi to alter his prayer. Thus, Kumbhakarna is said to have asked for “nidrasana” (a bed for sleep) instead of “indrasana” (Indra’s throne). Bramha granted the wish. Upon Raavana’s intervention, Bramha clarified that Kumbhakarna would sleep like the dead for six months at a stretch, wake up, satisfy his enormous appetite, and go back to sleep.
Please read this article for a scientific corroboration of Kumbhakarna’s symptoms and an actual medical condition.
Sleeping giant
As the battle between Raavana and Raama progressed and Raavana began losing most of his key players, Raavana decided that it was time to get the support of his powerful brother. He made arrangements to wake up Kumbhakarna, who is said to have been gigantic*. Cooked meat, aromatic food, blood and other liquids, sounds of trumpets, jabs of prods, and various other techniques were employed unsuccessfully. Finally, hundreds of elephants supposedly walked on him and successfully awakened him.
Once awake, Kumbhakarna ate, drank and then understood the purpose of having been awakened. He chided Raavana for his adharmic act of keeping Sita in captivity. Knowing fully well that Raavana was in the wrong, he fought on his side, due to brotherly love and loyalty.
*may have been used as a hyperbole, to indicate his strength, power and insatiable appetite.
He struck terror among the army of Vaanaras, wreaking havoc, killing thousands of Vaanaras, indiscriminately swallowing Vaanaras and Raakshasas, capturing Sugriva... When Lakshmana could not defeat him*, Raama, stepped forward and cut off his limbs. Despite this, Kumbhakarna continued to fight. Finally Raama, invoking the Indraastra, decapitated him. With his death, Raavana lost his confidence and realised that his doom was near.