Who is Vibhishana in Ramayana?

We all know that Vibhishana is Ravana's brother and an ardent devotee of Lord Ram. But we all don't know the actual story of Vibhishana.

Vibhishana, was the half-bother and the youngest brother of Ravana, the demon king who ruled over Lanka. Though he was a demon by birth, he had the qualities of a Brahmin as his father was a Brahmin. After Ravana captured Sita, Vibhishana advised him to return her back, but Ravana was deaf-ears and was not ready to hear to any of his advice. So Vibhishana declares that he would leave the kingdom. But if Ravana knows about his plans then he would be in danger,  so he flees away from Lanka. But before fleeing away from Lanka he calls his daughter Thirijata, who was guarding Sita in the Ashoka Gardens, and advises her to take care of Sita and his wife and Thirijata's mother Sarma very well, until Lord Rama defeats Ravana. Only, Thrijata and Sarma knew that Vibhishana had planned to join Lord Rama.

When he leaves to meet Rama Vibhishana knew very well for what he was destined. So, while going across the ocean he carries his mace along and is accompanied by two of his favourite demons. But actually it is said that if one needs to surrender he is not supposed to carry any weapon. But Vibhishan had a purpose on carrying his mace. When he reaches the shores of Rameshwaram where Lord Ram, Lakshman, Sugreev, Hanuman and others of the monkey troop are seated, Lakshman, Hanuman and Sugreev seeing the mace in Vibhishana's hand think that he had come to attack them. But as soon as Vibhishana sees Lord Rama, he dismisses his accompanies and falls on his feet. Seeing, the mace in his hand Lord Rama understands for what Vibhishan had brought the mace and also understands the reason for his birth in the world. His internal eyes open. He understands that Vibhishana is none other than his own Mace (as Lord Vishnu has a mace in his hand), Lakshman is his Adishesha and the Conch shell and the Chakra are none other than Bharata and Shatrugna. It is said that whenever Lord Vishnu takes an avatar in this world to destroy the evil his accompaniments are also born as some human and help him out throughout his journey to fight evil.