Thralls of the ironborn may only be obtained by paying the "iron price" (capturing them by raiding) under the Old Way. They are not slaves since they may not be sold and they may not be obtained by paying the "gold price." Their children may be free if they are drowned to the Drowned God. Thralls are used for farming and mining, activities which the ironmen consider unsuitable for free men. Thralls are forbidden in Braavos.
Thralls were commonly used by the First Men who ruled Westeros prior to the Andal invasion. For instance, Morgon Banefort, the Hooded King of Banefort, used thralls in his twenty-year war against Loreon I Lannister, King of the Rock. Some of the First Men of the Vale who did not submit to House Arryn after the Battle of the Seven Stars were reduced to thralls.
As time passed, however, thralldom was only practiced by ironborn of the Iron Islands. After Lord Lymond Hightower of Oldtown defended against the ironborn king Theon III Greyjoy, Lymond temporarily used thralldom to punish the captured ironborn through forced labor.
There were at least two thrall rebellions against House Greyiron. King Harmund III Hoare was considering outlawing thralldom in the isles when the Shrike began a successful revolt of the priests against his rule. Lord Quellon Greyjoy outlawed thralldom and freed the thralls of the isles, but this was reversed by his son and successor, Balon Greyjoy.
The man who owns a boat need never be a thrall, for every captain is a king upon the deck of his own ship.
- Archmaester Hake
- A Feast for Crows, Chapter 29, The Reaver.
- The World of Ice & Fire, The Iron Islands.
- The World of Ice & Fire, The Free Cities: Braavos.
- The World of Ice & Fire, The Westerlands.
- The World of Ice & Fire, The Vale.
- The World of Ice & Fire, The Iron Islands: Driftwood Crowns.
- The World of Ice & Fire, The Iron Islands: The Iron Kings.
- The World of Ice & Fire, The Iron Islands: The Black Blood.
- The World of Ice & Fire, The Iron Islands: The Old Way and the New.
- A Feast for Crows, Chapter 11, The Kraken's Daughter.
- A Feast for Crows, Chapter 18, The Iron Captain.