From the Wikipedia page 
Sir John Langstrother (died 1471) was Treasurer of England, prior of the Knights of St John in England, and Preceptor of Balsall.
A son of Thomas Langstrother of Crosswaite, he was by 1453 a councillor of the Yorkist king Edward IV. He was an administrator of the Knights of St John of Jerusalem and on 9 March 1469 was unanimously chosen as Prior of England, the Order's chief officer in the kingdom. Following the defeat of Edward's supporters by Warwick in 1469 at the Battle of Edgecote Moor he was appointed Treasurer of England by the short-lived regime of Duke of Clarence and the Earl of Warwick, but was dismissed by Edward when he regained power later in the year. He was reinstated in 1470 after the temporary re-accession of Henry VI, who had been restored with the help of Clarence and Warwick.
After the Yorkist victory at the Battle of Tewkesbury in 1471, where he had shared command of the Lancastrian centre, he sought sanctuary in Tewkesbury Abbey but was taken out and executed in Tewkesbury town centre. He was buried in the hospital of St John at Clerkenwell.