4. Vibhishana – Also known as Bibhishana, he is the younger brother of Ravana. His lineage is thus:
Out of the seven great sages (Saptarshi), who are supposed to be sons of Brahma, one of the rishis was Pulatsya. His son was Rishi Vishrava. Vishrava married Idavida, daughter of Rishi Bharadwaja. ldavida bore Vishrava a son, Kubera, the Lord of Wealth and the original ruler of Lanka. The accounts of Vishrava's far-reaching Yogic powers reached the ears of the Asura, Sumali, and his wife, Thataka. They got their daughter Kaikesi married to Vishrava. Vishrava fathered four children with her – Ravana, Kumbakarna, Vibhishana, and a daughter, Soorpanaka. Ravana would eventually oust his half-brother, Kubera, as King of Lanka and usurp his throne.
Vibhishana was the youngest brother of Ravana. He had differences with Ravana for a long time. When Rama came searching for his wife Sita, Vibhishana’s mother Kaikesi advised Vibhishana to join Rama. In the Lanka War, Vibhishana's knowledge of the secrets of Lanka were invaluable to Shri Rama. After the War, Rama made Vibhishana the ruler of Lanka.
When Rama was about to leave Ayodhya at the end of his reign, he told Vibhishana to stay on Earth and serve the people and guide them to the path of truth and Dharma. Hence, Vibhishana is considered one of the eight immortals, or Chiranjeevins.
In Mahabharata, there is a passing reference of Vibhishana. During the Rajasuya Yagna of Yudhishthira, when the remaining four brothers conducted campaigns in four directions for their oldest brother, Sahadev went southwards. He wanted to win friendship of the rakshasa king Vibhishana of Lanka – for which he sends Ghatotkacha (Bhima’s son from rakshasi Hidimba) as his envoy. Vibhishana honors Ghatotkacha and sends him back with a lot of gifts, gold etc.
There is not much that is heard of Vibhishana after that. It seems he is still supposed to rule Lanka.