- "Anyway, it's not my father I'm worried about. It's the Iron Bank of Braavos. We owe them tens of millions. If we fail to pay these millions, the Bank will fund our enemies. One way or another, they always get their gold."
- ―Tyrion Lannister
The Iron Bank of Braavos is a bank in the Free City of Braavos. It is arguably the most powerful financial institution in the Known World, with clients across Essos and Westeros, including the government of the King of the Andals and the First Men who rules over the Seven Kingdoms.
After taking over the role of Master of Coin from Petyr Baelish, Tyrion Lannister discovers that Baelish has been funding the Iron Throne's budget by borrowing massive amounts of money from several sources, including the Iron Bank of Braavos, to which the crown owes tens of millions of Gold Dragons. Tyrion is concerned because the Iron Bank has a tradition of funding the enemies of rulers who fail to repay their debts.
In the books
In the A Song of Ice and Fire novels, the Iron Bank of Braavos is the most powerful banking institution in the known world, richer and more powerful than the banks of all the other eight Free Cities combined, and with a fearsome reputation when collecting debts. When princes or kings default on their debts or are foolish enough not to honor their agreements with the Iron Bank, new princes and kings appear with the Iron Bank's support. These new princes and kings then honor the previous debt along with paying back the money the bank loaned them in claiming their new power, lest they suffer the same fate as their predecessors. "The Iron Bank will have its due" is a common saying among Braavosi.
- Iron Bank of Braavos at A Wiki of Ice and Fire (MAJOR spoilers from the books)