Manthara in Ramayana was the old maid servant of queen kaikeyi. Her real name was Kubaja and she had three curves in her body. It was Manthra who instigated queen Kaikeyi to stop the consecration of Sri Ram as the king of Ayodhya. It was she who reminded the queen about the two boons that Dasharatha had given her.
It is said that the three curves in the body of Manthara represents her evil nature. She has a cunning mind, she talks cunningly and her actions are also cunning.
She poisoned the mind of Kaikeyi by telling her that she and her son, Bharata, will be sidelined once Sri Ram becomes the king. It will be Kousalya, mother of Sri Ram, who will be ruling the palace. She asked Kaikeyi to make Bharata the king of Ayodhya by using one of her boons. She also gave the idea of exiling Sri Ram for 14 years.