Fall of the Night's King

The Fall of the Night's King was a battle that took place in the Age of Heroes.

Prelude
The thirteenth Lord Commander of the Night's Watch found in the Haunted Forest a cold woman with bright blue eyes, seemingly a female White Walker. He brough her back through the Wall and declared himself "Night's King" and her his Queen. For thirteen years they ruled over his brothers in the Night's Watch, making human sacrifices.

Battle
The Free Folk rallied behind Joramun, the King-Beyond-the-Wall and marched against the Nightfort, which the Night's King had taken as his seat, defeating him with the aid of House Stark.

Aftermath
The Night's King and Queen were both killed for the crimes, releasing the Night's Watch from their dominion. Afterwards, the Free Folk were unceremoniously forced back Beyond the Wall.

In the books
In the A Song of Ice and Fire novels, the King in the North (said to be the Night's King's brother) and Joramun, the King-Beyond-the-Wall formed an alliance to defeat the Night's King and free the Night's Watch from his rule. After his fall, when it was discovered that he had been sacrificing to the Others (possibly in a similar way to Craster), all records of him were destroyed and his very name was forbidden. It is likely this led the lords of the North to forbid the Night's Watch to construct walls at their keeps, ensuring the keeps would always be accessible from the south.