From the longer Wikipedia page 
Humphrey Stafford, 1st Duke of Buckingham KG (15 August 1402 – 10 July 1460), an English nobleman, great grandson of King Edward III on his mother's side, was best known as a military commander in the Hundred Years' War and in the Wars of the Roses.
The Privy Council was controlled by Edmund Beaufort, 2nd Duke of Somerset from around 1451. Buckingham supported Somerset, trying to maintain peace between him and Richard Plantagenet, 3rd Duke of York. However, from August 1453, the king became catatonic and York was appointed Protector of the Realm; when the king recovered in 1455, reversing many of York's decisions, war broke out. Although loyal to King Henry VI, Buckingham was reluctant to take up arms for Somerset, even though his son was married to Somerset's daughter. He seemed to be the ideal choice to negotiate and secured Somerset's release from prison in Feb 1455; he was still trying to get a compromise up to the eve of the First Battle of St. Albans on 22 May 1455. Buckingham commanded the king's army of 2,500; only about 50 people died in the battle, but this included Somerset. Buckingham himself was wounded (Michael Hicks, The Wars of the Roses, (Yale University Press, 2010), 110.) and captured with the king when the Earl of Warwick scored a remarkable success. York now had the political upper hand, made himself Constable of England and kept the prisoner, returning to the role of Protector when the king became ill again. Throughout all of this, Buckingham kept an open mind and helped maintain a relative stability during York's second protectorate.
Unfortunately, his actions estranged him from Queen Margaret. He opposed her decision to dismiss his half-brothers, Henry and Thomas Bourchier, from office and she disliked his decision to support York in military situations. But at the end, he aligned himself with the queen, escorting her to the 'Loveday' reconciliation effort held between the factions on 2 March 1458. When hostilities started again, his presence at Battle of Ludford Bridge led to the defeat of the Yorkist forces, and he was rewarded by Lancastrians with extensive grants from the estates of Sir William Oldhall.
Warwick regrouped and landed in Sandwich in June 1460. in the lead up to the Battle of Northampton, envoys were sent to negotiate, but Buckingham was no longer conciliatory. Buckingham informed them "The Earl of Warwick shall not come to the king's presence and if he comes he shall die" and told a group of Yorkist bishops that they were not men of peace but men of war and there could be no peace with Warwick. The battle was fought on 10 July 1460 and was shortened when Edmund Grey, 1st Earl of Kent turned traitor to the king and ordered his men to lay down arms, allowing the Yorkists access to the camp. In the ensuing fight, Buckingham, the Earl of Shrewsbury and Lord Egremont and John Beaumont, Viscount Beaumont, were killed by a group of Kentishmen. Buckingham was buried shortly after at Grey Friars, Northampton.