Task: Question Answering
Input (English): Passage: When Richard II was crowned in 1377, he led a procession from the Tower to Westminster Abbey. This tradition began in at least the early 14th century and lasted until 1660. During the Peasants' Revolt of 1381 the Tower of London was besieged with the King inside. When Richard rode out to meet with Wat Tyler, the rebel leader, a crowd broke into the castle without meeting resistance and looted the Jewel House. The Archbishop of Canterbury, Simon Sudbury, took refuge in St John's Chapel, hoping the mob would respect the sanctuary. However, he was taken away and beheaded on Tower Hill. Six years later there was again civil unrest, and Richard spent Christmas in the security of the Tower rather than Windsor as was more usual. When Henry Bolingbroke returned from exile in 1399, Richard was imprisoned in the White Tower. He abdicated and was replaced on the throne by Bolingbroke, who became King Henry IV. In the 15th century, there was little building work at the Tower of London, yet the castle still remained important as a place of refuge. When supporters of the late Richard II attempted a coup, Henry IV found safety in the Tower of London. During this period, the castle also held many distinguished prisoners. The heir to the Scottish throne, later King James I of Scotland, was kidnapped while journeying to France in 1406 and held in the Tower. The reign of Henry V (1413–1422) renewed England's fortune in the Hundred Years' War against France. As a result of Henry's victories, such as the Battle of Agincourt, many high-status prisoners were held in the Tower of London until they were ransomed.Much of the latter half of the 15th century was occupied by the Wars of the Roses between the claimants to the throne, the houses of Lancaster and York. The castle was once again besieged in 1460, this time by a Yorkist force. The Tower was damaged by artillery fire but only surrendered when Henry VI was captured at the Battle of Northampton. With the help of Richard Neville, 16th Earl of Warwick (nicknamed "the Kingmaker") Henry recaptured the throne for a short time in 1470. However, Edward IV soon regained control and Henry VI was imprisoned in the Tower of London, where he was probably murdered. During the wars, the Tower was fortified to withstand gunfire, and provided with loopholes for cannons and handguns: an enclosure was created for this purpose to the south of Tower Hill, although it no longer survives. 
Question: Who abdicated?
Output (English): Richard II.