Pandu is the son of Vichitravirya and Ambalika. The biological son of Sage Vyas. Though he is younger than Dhrutarashtra, Pandu is coronated as king of Hastinapur, as Drutarashtra is born blind.
Pandu is described as tall, fair, broad shouldered, wide-eyed, handsome, courageous, and an independent person. Kunti chose him amongst so many other contestants as her husband in her swayamvar. It was the first wedding in years that had not been arranged by Bheeshm. Bheeshm still had his say by arranging Pandu's marriage with the beautiful Madri.
Months later, Pandu successfully completed the digvijay expedition. A feat not achieved by his father, and uncles, and Bheeshm. He had it all, a kingship, a kingdom, reputation as a fearful enemy, wealth from the digvijay, and two beautiful wives.
Fate had something else in store for him… a vaidya (doctor) diagnosed him as infertile. This blow did not crush him. The cure was worse than the disease. As he was infertile, by the niyog system, he would have to impregnate his wives through his brother. That would be Dhruturashtra. The blind, lustful, womaniser, big brother who felt nothing but jealousy for Pandu! All his life, Pandu would want to wipe the smile off Dhrutarashtra's face that said "My son will be the king of Hastinapur!" If he chose not to produce progeny, Dhrutarashtra's son would anyway be the next king. Pandu had to find some way out, and quickly.
Mahabharat says, Pandu accidentally killed a sage in the woods, who then cursed Pandu that he would not be able to produce progeny. Was the sequence of events other way round … the vaidya diagnosed Pandu infertile, and Pandu killed him so that the knowledge of his disease remained a secret.
Pandu did not inform anybody of his infertile condition. He just walked out with his wives to the Himalayas. No reason. He decided he would have sons by some other man of his choice. And then one day return with his sons to Hastinapur.
Pandu declared he was leaving for Himalaya. Dhrutarashtra did not stop him. Was it because he wanted the kingship? Bheeshm did not stop him. Was it because Pandu was too independent for Bheeshm to manipulate? Was it because Bheeshm could not give up the power he had been enjoying as a caretaker?
Once in the Himalayas, Pandu took his wives in confidence. Kunti and Madri agreed to cooperate. They had 5 sons. Their biological fathers remain unknown. There is ample reason to believe that they were the sages who lived in the Himalayas. So far everything had gone according to Pandu's plan. Now was the time to return and reclaim the throne.
On a fateful day, Pandu and Madri died in a tragic accident.
After traveling for 17 days, Kunti returned to Hastinapur with the dead bodies of Pandu and Madri. Pandu and Madri were given a royal funeral in Hastinapur. [Adi Parv, Sambhava Parv:CXXVII]
Pandu's 5 sons and Kunti were left without a claim to the throne of Hastinapur, without the riches they would otherwise have had. Pandu had left behind a legacy of a life long battle for his wife Kunti to fight.