|Title||Lady of Casterly Rock|
|Allegiance|| House Westerling|
|Born||At the Crag|
|Spouse||Lord Jason Lannister|
|Book(s)||The World of Ice & Fire (mentioned)|
- Not to be confused with Joanna Lannister, the wife of Tywin Lannister.
Johanna Lannister was the Lady of Casterly Rock through her marriage to Lord Jason Lannister. According to a semi-canon source she was a member of the ancient and then-prestigious House Westerling.
During the civil war known as the Dance of the Dragons, Lady Johanna's husband, Lord Jason Lannister, and his twin brother, Tyland, supported the greens. Jason led his banners and marched to the field in support of Aegon II Targaryen, but he was slain in the Battle at the Red Fork in 130 AC. Lord Dalton Greyjoy, known as the Red Kraken, then attacked the Westerlands and caused much damaged to the region. Johanna barred the gates of Casterly Rock, but Dalton sacked nearby Lannisport.
The ironborn squabbled over Dalton's succession after the Red Kraken was murdered at Faircastle a few years later. Since the Lannister fleet had been destroyed by the Greyjoys, Johanna allied with the lord admiral of the Reach, Ser Leo Costayne, to have the westermen invade the Iron Islands in 134 AC. When one of Dalton's salt sons was taken to Casterly Rock as a captive, Johanna had him gelded and made him her son's fool.