Here is a background to how Mantara or Kooni of the Ramayan fame was born.
The ten-headed Ravana became all-powerful due to the boon he received from Brahma.
The gods rushed to Brahma and sought relief from the demon.
Brahma told them that only the Supreme God, Vishnu, could slay Ravana.
Accordingly Vishnu was born to Dasaratha as Rama, and Sakra was sent to earth to beget monkeys and bears to help him.
All the other gods were asked to choose their roles in the drama to be played.
Brahma asked a Gandharvi (demi-god), Dundhubi by name, to be born as Manthara.
Her mission? To create confusion and trouble.