The daughter of the mighty Ashwapati, a long-term ally of Kosala, Kaikeyi married Dasaratha after the latter had promised her father that the son born of her womb would succeed him as King of Kosala. Dasaratha was able to make this promise as his first wife, Kausalya, was childless and not likely to produce a son of her own. Kaikeyi also remained barren for many years of marriage, as a result of which Dasaratha married Sumitra, the princess of Magadha, another kingdom with strong political ties to Kosala.
Kaikeyi's personality is worth examining and provides a strong clue to her motivations which later led to her insisting on the exile of her stepson from Ayodhya. As a young girl and the only sister to seven brothers, Kaikeyi grew up without a maternal influence in her childhood home. Her father had banished her mother from Kekaya after realizing that his wife's nature was not conducive to a happy family life. Amongst other things, due to a boon, Ashwapati was able to understand the language of the birds. However, this was accompanied by a caveat that if he ever revealed the content of bird speak to anyone, even his own mother, that he would forthwith lose his life. One day, the King and his Queen were strolling through the palace gardens when Ashwapati happened to overhear the conversation of a pair of mated swans. The conversation so amused him that he laughed heartily, instigating his wife's curiosity. Despite being aware of the fact that he could not divulge the content of the conversation to her, without losing his life, Kaikeyi's mother insisted on knowing the cause of the King's mirth. When Ashwapati realized that his wife cared little for his life or well-being, he had her banished to her parents' home.
Kaikeyi never saw her mother again. She was raised by her wet nurse, Manthara, who accompanied Kaikeyi to Ayodhya as a trusted maid upon her marriage to Dasaratha. Her father's treatment of her mother and the latter's subsequent exile led to Kaikeyi harboring a deep distrust of men in general and husbands in particular, and to considering their love as "fickle" and "passing" in nature. In addition, she was very insecure in her position as secondary consort to Dasaratha. She realized that Dasaratha deeply respected his Queen and Empress, Kausalya, and had only married her in order to produce the much-needed heir. To this end, Kaikeyi realized that her position in her husband's affections and esteem relied heavily on her ability to produce that heir. When she remained barren, she became increasingly insecure and realized that she could never win in her struggle for supremacy over Kausalya, although Manthara proved to be a great help in this regard. The older woman schemed constantly to further her own position at the Court. And since her position depended on Kaikeyi's status at Court, Manthara lost no opportunity to feed the young Kaikeyi's insecurity and jealousy of Kausalya, despite Dasaratha's obvious enchantment and love for all of his wives.
Manthara's scheming paid off when Kaikeyi was able to convinced her husband to take her along with him during a military campaign against Samhasura, an enemy of both Indra and Dasaratha. During a fierce battle between the two, the wheel of Daśaratha's chariot broke and Samhasura's arrow pierced the King's armor and lodged in his chest. Kaikeyi, who was acting as Dasaratha's charioteer, quickly repaired the broken wheel and then drove the chariot away from the battle field. She nursed the wounded King back to health. Touched by her courage and timely service, Daśaratha offered her two boons. However, Kaikeyī chose to ask those boons later. In addition, she became his favorite wife and finally gained ascendancy over Kausalya
Years passed and all three Queens produced sons. Rama, the son of Kausalya, was Dasaratha's favorite son. Rama was a loving, obidient child who followed his father's foot steps and revered Kaikeyi over his own mother, leading to the former's deep love and affection for him. When he turned 16 and was to be crowned King, Kaikeyi was delighted and as happy as she would have been had it been her own son, Bharata's, coronation. However, Manthara, worried that Kaikeyi would lose her status as Chief Queen at Court if Rama ascended the throne (making Kausalya the Queen Mother) decided to instigate trouble She fueled Kaikeyi's dormant jealousy and envy of Kausalya, reminded her that her son's coronation would give Kausalya her former status as the most important of Dasaratha's Queens and would cut Bharata out of the royal lineage for ever. Finally, Kaikeyi's ardent desire to retain superior status over Kausalya motivated her to demand the two boons granted to her years earlier by Dasaratha and to further remind him of his promise to Ashwapati that the son born of her (Kaikeyi's) womb should succeed Dasaratha as King of Kosala. In order to ensure that Rama would be no threat to her son, Kaikeyi further demanded the exile of Rama from Ayodhya for 14 long years, reasoning that this length of time would be enough for Bharata to consolidate his position as King of Kosala. .
But Kaikeyī's desire never bore fruit. After sending his son into exile, a grief-striken Dasaratha died of a broken heart six days after Rama left Ayodhya. She came to blame herself for this death. Furthermore, Bharata swore never to ascend the throne as it was his older brother's birth right. He further blamed her for his father's death and is said never to have addressed her as "Mother" again. Kaikeyi was said to have died a lonely and broken-hearted woman, estranged from her son, his wife (the cousin of Rama's wife, Sita) and their two sons, her only grandchildren.