Sir John Oldcastle was an English Lollard leader. From 1409 to 1413, he was summoned to parliament as Baron Cobham, in the right of his wife.

Lollardy, also known as Lollardism or the Lollard movement, was a proto-Protestant Christian religious movement that was active in England from the mid-14th century until the 16th-century English Reformation. It was initially led by John Wycliffe, a Catholic theologian who was dismissed from the University of Oxford in 1381 for criticism of the Roman Catholic Church. The Lollards' demands were primarily for reform of Western Christianity. They formulated their beliefs in the Twelve Conclusions of the Lollards.