Wikipedia
Ilavida or Idavida is a character in the Ramayana, as the stepmother of Ravana and the first wife of Vishrava. Vishrava was the son of Pulastya and the grandson of Brahma, the Creator.
The daughter of the Rishi Bharadwaja and the sister of the Rishi Garga, Ilavida was given in marriage to the Rishi Vishrava and bore him a son, Kubera who would eventually become the King of Lanka (present day Sri Lanka).
Vishrava left Ilavida after meeting, and falling in love with, the Asura Princess, Kaikesi, the daughter of King Sumali and Queen Thataka. Through Kaikesi, he fathered another four children, Ravana, Vibhishana, Kumbakarna and Soorpanaka.
When Ravana invaded Lanka and usurped his older brother Kubera's throne, a disgusted Vishrava left his demonic family and returned to Ilavida, never to see Kaikesi or her offspring ever again. Kubera fled to Devaloka (Heaven) where he was charged by Indra, the King of the Devas, to manage his treasury. Kubera is best known to Hindus, therefore, as not the erstwhile King of Lanka, but as the God of Wealth.