Believe it or not Knights evolved out of mercenaries employed by chieftains and/or other rulers. The earliest it goes back to is the 800s AD, and from that point mercs evolved and became knights by the 1100s AD. However knights still acted very much like their merc counterparts. If it wasn't for The tales of King Arthur written back in the 12th century then chivalry would have most likely not become a part of the knights' way of life.
I also found this which might help:
Mercenary groups first appeared in the 12th century, when they participated in the Anarchy (a conflict of succession between King Stephen and the Empress Matilda between 1137 and 1153).
In the 1180s, similar groups were integrated into the armies of the King of France under Philip II of France. These troops of seasoned mercenaries were organized and mobile, a valuable advantage during the battles of the time and were important elements of the armies of Henry II of England and his son, Richard I. King John, used them at the beginning of his reign, when he was richer and more powerful than the King of France. However, in 1204, he did not pay the mercenaries. Philip Augustus used them to overcome the Plantagenets.
The Tard-Venus pillage Grammont in 1362, from Froissart's Chronicles.
During the Hundred Years War between England and France there were intermittent hostilities punctuated by periods of truce, when soldiers would be laid off en masse. In the absence of civilian skills and opportunities many, especially the foreign soldiers, formed armed bands known as bandes de routiers or écorcheurs and made a living by pillaging the countryside of southern France until hostilities resumed. Similar events occurred in Spain and Germany. By the time of the Treaty of Brétigny (1360) the bands had grown in size to the point where they had evolved an internal structure and adopted romantic names. The Tards-venus (late-comers), led by Seguin de Badefol ravaged Burgundy and Languedoc and even defeated the forces of the Kingdom of France at the Battle of Brignais in 1362.
The Catalan Company, formed in Spain in the early 1300s, fought in the Byzantine Empire before ending up in what is now Greece and the Navarrese Company, also formed in Spain, which followed them there.
By 1356, free companies, men at arms, and brigands had spread throughout the country from the Seine to the Loire engaging in unlawful activities. They had especially infested the roads from Paris to Orleans, Chartres, Vendôme, and Montargis.
So I guess it's clear that Leon isn't from a mercenary company given the date in which LoI takes place. Nevertheless he is one -in a very small sense- as knights evolved from them of a long period of time.