Sir John Oldcastle (born about 1378 - died 1417) was a popular figure, a friend to Prince Henry (later Henry V) and a valuable leader in Henry IV's campaigns against the Welsh. Oldcastle is presumed to be the model for Shakespeare's Falstaff. It would seem that Oldcastle had all the makings of a long career at court.
But Oldcastle was a firm follower of the teachings of John Wycliffe, and his beliefs brought him into conflict with his king. In 1413 Oldcastle was accused of heresy for his Lollard convictions. He was brought to trial under the influence of Archbishop Arundel, but he refused to recant his beliefs. He was sentenced to death as a heretic, but the sentence was stayed by Henry V, who must have hoped he could convince his friend to recant. Oldcastle was imprisoned in the Tower of London, but he escaped, possibly with the aide of the king. But Oldcastle turned against his friend and began plotting to overthrow the monarchy, seize or kill the king and his brothers, and introduce sweeping religious and social reforms according to his Lollard beliefs.
Unfortunately, Oldcastle's Revolt (1414) was poorly organized, and it lacked any real support from influential nobles who might have been tempted to the Lollard cause. The plan was that a small number of men would enter Eltham Palace in disguise and seize the king. At the same time a second force of men would take London. A gathering of conspirators was set for St Giles Fields, in London. However, the number of men who assembled proved disappointingly small; somewhere between three hundred and one thousand in number.
The night before the attempt on the king was to take place a group of Lollards were arrested in a London inn. The plot was laid bare, but Oldcastle rather foolishly went ahead with his plans. Lacking influential backers, Oldcastle and his supporters were easily defeated by the king's men, Oldcastle himself escaped, and though pardoned, he remained in hiding for the next several years. Finally, in 1417 he was captured again, and this time there was to be no escape. Henry V was fighting in France, and unable - even had he been willing - to come to his friend's aid this time. Oldcastle was sentenced to death as a heretic and executed by being burned alive over a slow fire.
Though it is easy to admire Oldcastle for his staunch adherence to his sincere religious beliefs, the effect of the revolt was the exact opposite of what he would have wanted, and it had the worst possible consequences for Lollardy. Nobles who might have been predisposed to support the general aims of the Lollards became staunch opponents of the movement, which they now saw, not as a religious reform movement, but as an attempt to overthrow the established political order. The upper classes and intellectuals turned away from Lollardy, and the church and lay authorities began to crack down on the movement with great vigour. Lollards were suppressed and their numbers dwindled until the movement became little more than an historical footnote.
Note: One historian has claimed that Oldcastle was not involved in the revolt that bears his name, or at least only a peripheral figure. Paul Strohm, in his 1999 book England's Empty Throne: Usurpation and the Language of Legitimation, 1399-1422 argues that the Lancastrian monarchy desperately needed to legitimise itself - after all, Henry IV's claim to the crown rested more on his murder of Richard II than on any dynastic legitimacy. Therefore, the rebellion caused the nobility to close ranks and throw their support behind the monarchy, and against the perceived threat to their own interests posed by Lollardy. The suggestion, then, is that the Lancastrians intentionally allowed, or even connived at creating, a rebellion which they knew they could easily suppress.