|Born||In 285–287 AC, at Westerlands|
|Died||In 299 AC, at Riverrun|
The World of Ice & Fire (appendix)|
A Game of Thrones (appendix)
A Clash of Kings (mentioned)
A Storm of Swords (appears)
A Feast for Crows (appendix)
A Dance with Dragons (appendix)
Willem's hair are either long and blond or brown.
Lord Gawen Westerling once suggested that Willem or his twin Martyn marry Gawen's daughter, Jeyne. Ser Kevan Lannister refused this offer because he considered Jeyne of dubious blood due to the lineage of her mother, Sybell Spicer.
A Game of Thrones
Willem is part of the army of his cousin, Ser Jaime Lannister, that invades the riverlands. Willem and another cousin, Tion Frey, are captured during the battle in the Whispering Wood by the northern army of Robb Stark.
A Clash of Kings
Robb, now King in the North, and Tyrion Lannister, the acting Hand of the King, attempt to negotiate Willem's release. Robb offers Willem and Tion in exchange for Arya and Sansa Stark. Tyrion declines that offer, but offers Lord Medger Cerwyn and Ser Donnel Locke for Tion and Harrion Karstark and Ser Wylis Manderly for Willem. No agreement is reached.
A Storm of Swords
Torrhen and Eddard Karstark, the younger sons of Lord Rickard Karstark, were both killed by Jaime Lannister in the Whispering Wood. Rickard wants to kill Jaime in retaliation, but Jaime is released from captivity at Riverrun by Catelyn Stark without Robb's knowledge.
When Robb's host returns to Riverrun, Lord Karstark feels robbed of his revenge against the missing Jaime and chooses Willem and Tion instead. With some of his men, Rickard kills the boys and two of their House Tully guards. Catelyn observes that one of the boys was blond (presumably Willem as a Lannister), wore his hair long, and was trying to grow a beard. He was probably killed in his sleep. His cousin was brown-haired (presumably Tion as a Frey) and had fought for his life. Both were pale from their imprisonment.
Furious about the killing of his captives, Robb executes Rickard with his accomplices at Riverrun.
Robb: I saw your sons die, that night in the Whispering Wood. Tion Frey did not kill Torrhen. Willem Lannister did not slay Eddard. How then can you call this vengeance? This was folly, and bloody murder. Your sons died honorably on a battlefield, with swords in their hands.
Rickard: They died. The Kingslayer cut them down. These two were of his ilk. Only blood can pay for blood.
- See the Willem Lannister calculation.
- George R. R. Martin's A World of Ice and Fire, Willem Lannister.
- A Clash of Kings, Appendix.
- A Game of Thrones, Appendix.
- A Storm of Swords, Chapter 20, Catelyn III.
- A Storm of Swords, Chapter 19, Tyrion III.
- A Game of Thrones, Chapter 63, Catelyn X.
- A Clash of Kings, Chapter 25, Tyrion VI.
- A Clash of Kings, Chapter 55, Catelyn VII.
- A Storm of Swords, Chapter 2, Catelyn I.
- A Storm of Swords, Chapter 14, Catelyn II.