In the
Mahabharata,
Kunti is the daughter of King Sura of the Yadus. Her name is actually Prtha, and thus her sons are sometimes referred to as the
Parthas. Her brother is
Vasudeva.
Kuntibhoja adopts Prtha. She meets the sage Durvasa and he gives her a mantra which she can repeat to call down a god. She invokes it one day out of curiosity, to see if it will work. The Sun, Surya, comes down and begets a child on her.
God-begotten children in Hindu tales are usually born immediately, with no time out for pregnancy. So no one noticed that the unmarried teenage princess had a son. In fact, Surya restored Kunti's virginity.
Her son, Vasusena, or Karna, was born wearing earrings and armor. Ouch! Kind of takes away from the cool "born without an inconveniently long pregnancy" advantage.
Kunti casts the boy adrift in a basket in the river. He is rescued and adopted by a charioteer.
Kunti is married to King Pandu of the Kurujangala kingdom, and goes into exile with him. She uses the mantra with Dharma, Vayu, and Indra to have three sons: Yudisthira, Bhima, and Arjuna.
Kunti follows her sons as they gain a kingdom and then go into exile again. When Arjuna brings home Draupadi as his wife, she suggests that all five Pandu brothers become Draupadi's husbands.