“I sell my sword, I don’t give it away.”
Lore
A sellsword is a soldier who offers his services to the highest bidder. Most sellswords are professionals with combat experience. They are more common in Essos than in Westeros, as Westerosi lords prefer to raise feudal levies. The mercantile cities of Lys, Myr, and Tyrosh employ hired sellswords for protection. Some individuals, like Ser Jorah Mormont, turn to this profession after running out of money or being exiled. Many sellswords keep their valuable possessions, such as weaponry, armor, and silks, close at hand.
Sellswords often have a negative reputation. Some nobles see them as unchivalrous and pitiless. They are not allowed within the Black Walls of eastern Volantis and are infamous for betraying anyone for the right amount of gold. Sellswords, along with pirates and slavers, can be found in the Basilisk Isles.
Many sellswords belong to free companies, which are groups of mercenaries. Some of these companies, like the Golden Company, are known for their loyalty and discipline. Others, like the Brave Companions, are mere rabble seeking loot. Some captains are rumored to start conflicts during peacetime, and some companies attempt to conquer the Disputed Lands when not under contract. Members of these free companies often adopt names of extinct Houses from Westeros.
Reference: https://awoiaf.westeros.org/
