There absolutely were people who could be described as adventurers, but they're probably quite different from what you're imagining.

In the very Early Middle Ages, most of the successor kingdoms, especially the Frankish kingdom (what is now France), practiced an inheritance scheme whereby property was divided between male heirs without respect to birth order. This goes away at some point after the Carolingians, and by the High Middle Ages, the rule has become primogeniture; that is to say, the oldest son takes all, and the younger sons must make their own way in the world, or join the eldest son's household as a sort of perpetual juvenile. In the case of small peasant landholders, the landless sons would often go to towns or enter into a dependent relationship with a large landowner as a serf. But in the case of aristocratic and especially knightly households, such would be generally unthinkable. Their options were more limited: to join a lord's household as a dependent knight, to marry an heiress and so acquire her land, or receive land from a powerful aristocrat in exchange for vows of service. Further complicating things is the fact that at the time eldest sons came of age, their fathers were generally in the prime of life, and to remain at home would mean in effect to continue adolescence indefinitely.

Very commonly, groups of young, landless knights would go out into the world to make their way, usually led (and financed by) a son of a local lord, who might be funded by his father as a way of getting him and his restless young friends out of the neighborhood. While seeking land, they would attempt to practice the aristocratic arts of war through hunting, competing in tournaments and, effectively, doing mercenary service on behalf of kings or lords. These wandering bands of rootless men barely out of adolescence came to be the cause of much disorder, especially in northern France. They debauched themselves quite scandalously, spent recklessly, and were often impoverished as a result. An armed man will not willingly starve, not when he may steal, and as a result, they were quite as capable of terrorizing the peasantry as any band of ravaging mercenaries.

Well, it might be helpful to bring up the origin of the modern "adventurer" trope. It was mainly popularized by Dungeons and Dragons, which was itself heavily influenced by the works of J.R.R. Tolkien. And where did Tolkien, the noted Anglo-Saxonist, get it? Beowulf, to be sure.

In Beowulf lies the uncontested root of the modern idea of adventurer and adventuring party. The hero hears of a horrible monster in a distant land, and he and his bold comrades go on a quest to defeat it. He kills the monster with a magic sword and acquires treasure. If this sounds familiar, it's because modern fantasy is all extremely indebted to Beowulf.

What about real life? Did a historical Beowulf actually do those things? Well, probably not. But it plays on ideals which were very real in Anglo-Saxon society (and in other early medieval Germanic societies). A lord's loyal thegns were expected to do great deeds in their lord's service; in turn, the lord was expected to be a generous treasure-giver and protector.

You've probably noticed an important difference by now: modern fictional adventurers are often self-sufficient, while these Germanic warriors were expected to serve a lord. In fact, it was considered catastrophic not to have a lord to serve; there are multiple Old English poems about how awful it is to be adrift in the world with no lord. This disconnect is probably because Tolkien, in The Hobbit and The Lord of the Rings, did not emphasize that aspect. So there are some similarities between modern adventurers and the ideal of the early medieval Germanic thegn, but there are also significant differences.

For further reading, you could try Dorothy Whitelock's The Beginnings of English Society.

hi! not entirely sure whether you're including people like knights errant / mercenaries, but if so, you may be interested in these previous posts

mercenaries in medieval Europe:

• How do modern mercenary units (PMCs) compare in function and use to mercenaries active in Europe in the 13th-18th centuries AD?

• The Effectiveness of Mercenaries

• The evolution of mercenaries?

• How common and reliable were mercenaries in Europe between the Fall of Rome and discovery of America?

• Were there any renowned mercenaries during the Middle Ages?

• so Knights-errant are a common feature in fiction, but did some version of them ever exist?

• In medieval times, or later, were there ant well known adventurers or knights? Also, were they anything remotely similar as to how they're portrayed in games today?

• What are some of the best examples of a highly organized or disciplined mercenary/sellsword/privateer company from the 1000's or since?

• Were There Mercenary Knights Like Modern Mercenaries?

• Were opinions towards mercenaries as negative historically as they are today?

• What precipitated decline of European mercenaries?

life as a medieval European mercenary:

• How would medieval European rulers find and hire mercenaries? How did they contact these groups?

• How did you actually join a mercenary band?

• What kind of life did a mercenary have during the middle-ages?

• What was it like to be part of a mercenary group in Europe during the middle ages?

• [Europe, 12th-15th centuries] I am a mercenary captain with a good company of men under my command. How does my career look, what are my functions in the army once sub-indentured by a noble, and what is expected of me in battle?

"hedge knights" in Game of Thrones:

• Were hedge knights a real thing?

• How believable are the setting and events in A Song of Ice and Fire?

To tag along on this question.

What about the more exploratory trope of adventurer? The swash and buckle, discover a new land and find treasures/fame type?

A similarly described character as the mercenaries/noblemen in U/rittermeister but with more of an intent or goal. Reaching the holy land, stealing so and so's treasure etc.

I don't know if this is appropriate for r/history but it informs my question. U/rittermeister's description reminds me much of Mat Cauthon's description of mercenaries in Robert Jordan's WoT saga and I've always been fascinated by Mat's 'Land Pirate' character type as a foil to this. Similarly seen in games often as a 'Rogue' or 'Ranger' class. Another example would Cohen the Barbarian in Discworld.

Do we have any reputable accounts of people like this? I can think of Marco Polo or the North American explorers like Sir Alexander Mackenzie but they don't quite fit; any other examples?

Edit Found John Hawkwood in a earlier link. He is very interesting.

Stupid question, but would these young men terrorizing the peasantry wear any kind of metal armor? It seems like might be pointless against someone with a pitchfork, no pun intended.