The five Pandavas [the sons of Pandu], Yudishtira, Arjuna, Bhima, Nakula and Sahadeva, are the main protagonists in the epic and represent various aspects of "Good/Dharma". In the literal sense they were not Pandu's sons, as Pandu had been cursed to drop dead immedeately after having intercourse. They were in fact conceived by various deities on Pandu's wives: Kunti (Yudishtira, the eldest: Yama, Arjuna: Indra and Bhima: Vayu) and Madri (Nakula and Sahadeva: The Ashwins). Their main charecter treats being "inherited" from each particular Deity.

Of course it should be noted that Karna was in fact the eldest of the Pandava, having been conceived on Kunti by Surya, before Yudishtira. However this fact was held secret by Kunti and was only reveiled to Karna and later the Pandava's at the onset of the war.