Who was Vedvati for Ravana?

Vedavati was a really beautiful daughter of sage Kushadhwaja in Kritayuga. Her father wanted Lord Vishnu to accept his daughter as his wife. When he rejected all her suitors, a demon named Shambhu killed her father. Her mother also lost her life in grief. Now unprotected, she decided to do severe penance to get Vishnu as her husband. She went into the forest wearing matted locks and black antelope skin and started doing penances. Once Ravana who was on a tour saw her and proposed to her and rebuked her penance and called it unworthy for her as she was young and beautiful and not old , fat and ugly for whom penance is the only option as no one wants them.

She introduced herself and rejected his offer, she called herself Vedas personified. Ravana then grabbed her hair and she through power of her penance cut her hair through her hand and cursed Ravana. Humiliated by him she entered fire vowing to return back and avenge her insult.

Later, Vedvati was reborn on a lotus with fragrance of lotus. He brought her to his palace but his ministers seeing her body told him she would be his destruction. Angry Ravana threw her in the sea and she was taken by the sea to Mithila where Janaka found the baby in ploughed line and adopted her and called her Sita.

Sita was Vedvati reborn and later retellings due to this story spread the myth that Ravana was father of Mata Sita but that's not true. He lusted Vedavati and he brought her reborn form because he found the baby fascinating. If ministers had not warned him and he didn't throw baby Sita (Vedvati reborn) in the sea, baby Sita would be brought up in Lanka. What an irony. Ravana lost the opportunity to be father of Mahalakshmi and save his life.

Source- Uttar Kand, Valmiki Ramayana

Who was Vedavati in Ramayana?

Vedvati was a daughter of a Brahmrishi named Kushadhwaja in Kritayuga (Satyuga). This Kusadhwaja was a son of Brihaspati.

Vedvati was very beautiful and her hand was sought by everyone in marriage but her father gave her hand to no one because only Lord Vishnu was acceptable to him as his son in law. Due to this a Daitya named Shambhu became enraged and he killed her father while he was asleep in night. Her mother also died due to depression and grief on his funeral pyre. Due to this, Vedvati accepted only Vishnu as her husband in her heart.

When once Ravana was wandering in a forest in Himalayan region, he saw a beautiful female ascetic with matted hair and wearing black antelope skin.

He enquired about her family and praised her beauty. She told her entire story and he told her to stop penance as she was beautiful, young and should enjoy life and remarked that penance was for old and ugly ladies. He proposed her to be his wife which she denied.

She rebuked him for his proposal and angry he caught her hair. She now totally enraged cut her hair with her hand which remarkably became like a sword.

She immediately lighted fire and said she no longer desired to live being insulted in such a manner. She warned him that she would return as his doom and will be responsible for his death.

She says she would appear as Ayonija (not born from a womb) and as daughter of a pious man. She then entered the fire.

Suddenly celestial flowers started raining from heaven and she appeared again on a lotus with fragrance of a lotus.

Ravana took her and showed her to the ministers, seeing her features, ministers said if she stayed in your house, she will be your death.

Ravana angry by this threw her into the sea. She reached the shore and she came when Janaka was doing ritual ploughing for his Yajna, out of mother Earth.

So, Vedvati was reborn as Sita with the sole purpose of destruction and death of Ravana.

Source- Canto XVII, Uttar Kand, Valmiki Ramayana