The Visio Willelmi de Piers Plowman (ca. 1360-90) is a lengthy allegorical dream poem written by a master poet thought to be named William Langland and revised by him over a period probably spanning about two decades. It is not in any way a folkloric product, but its themes permeated the popular culture.
Piers Plowman is a moralistic story of a man who dreams of the titular Piers, who offers to guide him in finding the truth; he subsequently seeks enlightenment through three characters named Dowel, Dobet (transparently short for "Do-better"), and Dobest. Along the way, however, Langland also presents us with a compelling view of contemporary society, and this was not overlooked by his contemporaries, who appropriated the title character for reasons of social commentary.
At the time of publication, Piers Plowman was anonymous. It came to be associated with the Lollards, and this is likely why it is one of the few notable pieces of Middle English literature never to have been printed by William Caxton.
Many later medieval poems exist which also center on the character of Piers Plowman, and the earliest were definitely Lollard works. Most were also in alliterative verse, part of the late medieval "alliterative revival" which saw a resurgence of such forms in English literature; in this, they match the artistic style (but seldom the talent) of Langland. In the sixteenth century, many of these poems (nearly all of which date from before 1450) began to be printed for the first time, as were various editions of Langland's original (often misattributed to Chaucer or Wycliffe), and new Piers Plowman poems began to be composed once again. Some printers, feeling the incompleteness of Chaucer's Canterbury Tales an unconscionable defect, supplemented the Tales with other material, often including Piers Plowman poetry they thought to be the work of the same author.
The audience for Piers Plowman poetry may have been working people, but their education in spiritual matters is generally presumed to be significant; many of the works drawing on Langland contain nuanced denunciations of specific orders of friars and other detailed criticism of the Catholic Church. One, The Praier and Complaynte of the Ploweman unto Christe, specifically depicts Piers petitioning the Lord to reform His Church as well as society more generally.
It's not surprising, then, that Piers Plowman material is often also concerned with social justice. Lollardy was a populist movement precisely because it was tied so closely not only with specific points of theology but because of its emphasis on Christ's concern for the poor; while traditional clergy attacked the Lollards on points of doctrine such as their heterodox view of Communion, the Lollards saw much greater import in the fact that the clergy were the tools of a deeply unjust social order which, they believed, was roundly condemned in the Bible.
One of the few known authors of Piers Plowman material, owing much to this tradition, is the Lollard priest John Ball. As one might suspect, a common theme of Ball's writings and preaching was social equality, and he is known to have been quite radical on that score. He is best known for the quote "When Adam delved and Eve span, who then was the gentleman?" But the sermon from which that couplet is taken continued, declaring that "if God would have had any bondmen from the beginning, He would have appointed who should bond, and who should be free. And therefore I exhort you to consider that now the time is come, appointed to us by God, in which ye may (if ye will) cast off the yoke of bondage." (I have found this quote in multiple secondary sources but am unable to locate the original Middle English version.)
That sermon was delivered at Blackheath in 1381, to a gathering of peasants and tradesmen and village officials already prepared to revolt. Ball's words fell on receptive ears, for the politics of the assembled crowd were decidedly edging toward a medieval form of what we would now call communism. Lollard theology and populist resentment against the feudal order (and the high taxes it imposed to pay for the Hundred Years' War) had come together to create a movement, planned and organized in secret, which carried out the largest peasant revolt of the medieval period, which subsequently came to be known as the Great Rising. The workers demanded an immediate end to the institution of serfdom and to the imposition of central government (favoring the idea of self-governing local villages under what they termed "the Law of Winchester"), broke down the walls of local jails, burned records of court cases and tax debts, and ultimately marched on London. There, they captured the Tower of London, and King Richard II felt compelled to meet with the rebels, and apparently offered some concessions. The leadership of the revolt was unsatisfied, however, and the King agreed to a private audience, at which his guards killed the rebels he was meeting with. (Chronicles from the time state that they had attacked Richard, and the guards acted in defense of their King.) The uprising was then able to be put down without difficulty, and the King is said to have promised that the rebellious rustics would return to bondage, "not as before, but incomparably harsher."
In planning the Great Rising, the leaders of the movement corresponded in secret. The event was not a spontaneous one, but the work of a vast conspiracy, organized by means of secret letters written under various pseudonyms. The chief architect of the events was known as Wat Tyler, which may or may not be his real name; a few historians have even suggested that Tyler was a pseudonym for none other than John Ball, though sources from the time of the Rising tell us of the two dying separate deaths (Tyler at the hands of the royal guards, and Ball by hanging the following month). Another name frequently found in connection with the revolt was Jack Straw or John Rakestraw, which seems to have been a collective pseudonym for several populist leaders (probably including both Wat Tyler and John Ball at various times) but was sometimes understood as an individual person. Still others chose to use a false name taken directly from the literature that best captured their feelings about the injustice of feudal society: Piers Plowman.