There’s the common story of the heroic commoner being knighted and granted land, but in all my amateur reading of the medieval era, the only example I know of is John de Coupland, and I’m not even certain he was a commoner. While I requested England I’m curious in general.
While it wasn't particularly common, there were certainly some examples from 14th century England beyond John de Coupland. The most famous, and the one who rose to the highest levels of command and wealth, is of course Sir John Hawkwood. Although not from the gentry, John Hawkwood wasn't exactly of humble birth, and his father had extensive lands throughout Essex and many connections with the local gentry. Although not the wealthiest man in Sible Hedingham, where Hawkwood likely grew up, or Finchingfield, where Hawkwood reappears in the 1350s, Gilbert was nonetheless one of the wealthiest men in either village and we have documents showing him arguing court cases over hundreds of acres of land. The elder John Hawkwood, who inherited all his father's property would remain as a "franklin", one step below the gentry, throughout his life, although this may have been from choice rather than actual wealth.
Not much is known about the young John Hawkwood, beyond that he received £25 cash and a quantity of grain, in his father's will and that he was an apprentice (most likely to a hosier) in London. William Caferro speculates, based on later personal and geographic connections in his life, that Hawkwood initially served as a mounted archer with members of the Liston, Coggeshale (most likely) or Bourchier families, under William Bohun, the Earl of Northampton, in Brittany in 1342. No records exist in sufficient detail to confirm this, but if he did serve under Bohun then Hawkwood likely also fought at Crecy, Winchelsea and Poitiers.
A John Hawkwood appears twice in the Essex Sessions of the Peace in 1350 and 1351. In the first case, he and another man beat a third to within an inch of his life and were fined, while in the second instance he "borrowed" a neighbour's horse to plough his field and was also fined. It's theoretically possible that this refers to the elder John Hawkwood but, as he preferred Gosfield to Finchingfield (where the offences occurred) and went out of his way to stay out of the public eye, it's likely that the younger John Hawkwood was involved in the rather petty and non-knightly behaviour.
In 1360, when the Great Companies stormed Pont-Saint-Esprit, Hawkwood was a "poor knight" without the reputation of other captains but enough influence to be a "corporal" leading perhaps 160 men. How or why he was knighted is entirely unknown, but he'd married, possibly to a junior member of the de Vere family, and had a daughter by this time.
However, once in Italy Hawkwood prospered. He rose to command the White Company and, even when it broke up, his English Company was famous and widely sought after. He played a prominent roll in all the Italian wars of the period, often directing the entire campaign, and eventually married the (illegitimate) daughter of the Milanese ruler Bernabò Visconti. Although not always flush with cash, Hawkwood did manage to amass numerous properties in England and Italy and was one of the wealthiest military men of his day.
Hawkwood is perhaps the commoner who rose the highest, but other examples, such as Robert Knolles and Sir Robert Salle, rose to knighthood and gained considerable reputations as captains. Robert Salle, in particular, rose rather high as he may have originally been a serf and lacked the connections to the gentry that Knolles and Hawkwood had. The connections to the gentry and nobility, with their wealth and influence, is almost certainly one of the key factors in the rise of most mounted archers to men-at-arms or knights.
Other archers quite likely advanced to, if not the gentry proper, at least to a high level of wealth for a commoner, with the mid-14th century chronicler Thomas Grey noting that "many" archers advanced to being men-at-arms, although the evidence for this is hard to come by thanks to patchy medieval records and a general lack of focus in the period on archers as individuals. It's also made more difficult by the practice of younger or poorer family members serving as mounted archers, and these may have been the archers who most often became men-at-arms.
The takeaway, I think, is that the story of the heroic commoner who was knighted and granted land is certainly possible and did happen, but it wasn't particularly common. More likely, particularly well connected, brave or effective commoners could and did rise to a sufficient level of wealth to serve as a man-at-arms and live as the upper levels of the commoners or the lowest levels of the gentry, which is a much less romantic story and naturally attracts less in the way of novels.
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