Shalya
Shalya (Sanskrit: शल्य, lit. pointed weapon) was the brother of Madri (mother of Nakula and Sahadeva), as well as the ruler of the Madra kingdom. Shalya, a powerful Spear fighter and a formidable charioteer, was tricked by Duryodhana to fight the war on the side of the Kauravas. Shalya was an incredibly calm and deliberate fighter, which is why he made a good charioteer and why he could excel at mace-fighting despite his slight build.
According to a version of Mahabharata (which is not included in the BORI Critical Edition), on his way to Hastinapur, Pandu encountered Shalya's army, and Pandu was very much impressed with Shalya's General. Shalya proposed that they could either decide the victor by war, or, by marriage. He then revealed that his General was none other than his sister Madri. Looking at her beauty, Pandu accepted her willingly and took her to Hastinapur.
Years after Madri had's death, Shalya, each year, brought his nephews Nakula and Sahadeva to Madra, desiring to make them his heirs. On their eighteenth birthday, Shalya revealed his intention to the twins. Shalya argued that Nakula could be a king one day, instead of fourth-in-line to the throne of Hastinapur...provided that Yudhishthira was named the crown prince of Hastinapur. The wise Nakula pointed out that Shalya only wanted Nakula and Sahadeva as his heirs, because both were children of Gods and in fact, Shalya was eschewing his own children with this gambit. Nakula claimed that while he and Sahadeva staying with the Pandavas would give them no power, his brothers and Kunti genuinely loved him, and would never try to make Nakula and Sahadeva their pawns. Through some deliberation, Nakula is convinced that Shalya is being genuine. He and Sahadeva become the heirs to the throne, but Sahadeva told his uncle on one condition: they will always stay with the Pandavas. This story is not included in BORI's Critical Edition of Mahabharata.
When Shalya heard of the impending Kurukshetra War, he marched forth with his army to join his nephews. On the way, Shalya was tricked by Duryodhana, who arranged a huge feast for Shalya and his men, entertaining him for hours. Impressed, Shalya was generous with his praise and asked to see the host, thinking that it was Yudhishthira. When Duryodhana revealed the treachery, Shalya is astounded but is compelled to grant a boon due to the hospitality. Unable to turn down Duryodhana's request to join the Kauravas, Shalya met the Pandavas and apologized for his mistake.
Prior to the start of the war, Yudhishthira met with his elders on the Kaurava side, asking for their blessings. Shalya readily gave his blessings to Yudhishthira, blessing him with victory. He requested Yudhisthira to ask for a boon. Deducing why Duryodhana had desired Shalya in the first place, Yudhishthira demanded from Shalya that he would demoralize Karna and dampen his spirits when he eventually became Karna's charioteer. Shalya promised to do so.
Though not spirited in his fight, Shalya confronted many great warriors during the war. Shalya killed Uttar Kumara on the first day of the war. Shalya killed the boy with his spear after a fantastic duel; Shalya saluted Uttara's brave death. On the fourteenth day of battle, Shalya was charged with keeping Jayadratha away from Arjuna. Shalya attempted to check Arjuna's advance. Arjuna responded by tying Shalya's to his chariot using his arrows, much in the same way Abhimanyu had done the day before.
On the 16th and 17th days of the war, Shalya served as Karna's charioteer, while continuously praising the Pandava prince and citing Karna's shortcomings. On the 16th day, Karna is fighting Arjuna and has the upper hand. He aims the Nagastra at Arjuna. Shalya interrupts, telling Karna to aim at Arjuna's chest. Disgusted at Shalya's constant praise of Arjuna, Karna thinks that that advice must be inaccurate, and aims at Arjuna's head. Krishna pushes Arjuna's chariot into the ground; the astra only takes off Arjuna's crown instead of his head.
During the next day's battle, Karna defeats but spares Nakula and Sahadeva, saying that they are younger and not his equals, therefore not deserving of death by his hands. Against his will, Shalya finds his respect for Karna growing. Still desiring Arjuna's victory, he continues to deride Karna, and doesn't come to Karna's aid when, during the epic fight with Arjuna, Karna's chariot-wheel gets stuck in the mud. In the end, Arjuna kills an unarmed and disadvantaged Karna with the Anjalika weapon.
While reporting the events to a desolate Duryodhana, Shalya cannot help but rage at Arjuna for his cowardice, while praising Karna's character. Though he was reluctant to be Karna's charioteer, considering it a slight that a kshatriya should serve a charioteer's son, Shalya concludes that Karna's conduct not only proves that he belongs on the battlefield, but proves that Karna is one of the foremost fighters of his time. Duryodhana names Shalya as the commander-in-chief.
After Karna's death, Shalya, now impassioned to fight for the Kaurava cause, takes over as the commander of the Kaurava forces, rallying them from retreat. Krishna suggests that Yudhishthira should kill the powerful warrior because the eldest Pandava was not a man of aggression and could meet Shalya's coolness in battle. Shalya is killed by Yudhishthira in spear-combat. After Shalya, Nakula becomes the king of Madra kingdom.