From the very beginning of Game of Thrones, the Lannisters have been tied to money. The saying "a Lannister always pays his debts" has been repeated many times. But in "The Queen's Justice", we see Cersei Lannister facing her money woes with the Iron Bank. So what is the Iron Bank and why is it so important? Here are three important things to know about the bank's past . . . and its future.
The bank has funded the Lannisters greatly.
It's actually the Iron Bank of Braavos, and it is a financial institution that has many clients, including the government that rules over the Seven Kingdoms. It especially has ties to the Lannisters and Baratheons, given how much they owe. In season one, Ned Stark is shocked to find out the Iron Throne owes 6 million Gold Dragons. The institution is also infamous for the line "the Iron Bank will have its due," so it's not to be messed with.
We also see the Iron Bank in season three, when Petyr Baelish becomes Master of Coin and is borrowing more money from the Iron Bank. This worries Tyrion Lannister because the Iron Bank has no problem funding his family's enemies.
The bank also funded Stannis Baratheon.
In season four, Stannis Baratheon also turns to the Iron Bank, to continue his failed mission to take the Iron Throne. He and Ser Davos go to Braavos to convince the bank that they are its best option to getting its money back after the death of Tywin Lannister. They are successful and get a loan, but it ultimately is another loss for the bank, given Stannis's death.
The bank may invest in Daenerys Targaryen.
The visitor from Braavos reveals that the Iron Throne's vaults are empty, and given it's fighting a new war, it will be needing more money. It also doesn't help that the rich Tyrells are no longer allies but enemies. So it makes sense that the Iron Bank would be interested in backing Daenerys instead.
Cersei asks for a fortnight to pay her debt in full, and given her lead in victories, she might get to keep the Iron Bank on her side.