Jon Arryn

Jon Arryn is a character who is deceased when the events of Game of Thrones begins. It is not known if he will appear in flashback or not.

Lord Jon Arryn was the ruling lord of House Arryn, one of the Great Houses of Westeros. Many years ago he fostered both Robert Baratheon and Eddard Stark, and came to love both as replacement sons after his own children died at a young age. When the Mad King condoned the kidnap of Eddard's sister (and Robert's betrothed), Lyanna Stark, and demanded that Eddard be turned over to the King's justice, Lord Jon Arryn rebelled, calling his banners to war. House Stark and House Baratheon followed suit. The rebels forged an alliance with House Tully through marriage, with Eddard married to Catelyn Tully and the then-elderly Jon to the young Lady Lysa Tully.

After the rebel victory in the war, King Robert appointed Jon as Hand of the King, a position Jon executed well for many years. He dies immediately prior to the events of the series, sparking King Robert's search for a replacement. Jon Arryn is survived by his wife Lysa and their six-year-old son, Robert Arryn.

In the books
In the Song of Ice and Fire novels Jon Arryn is a great lord, wise counsellor and canny tactician. He is loved as a second father by both Eddard and Robert, and commanded great respect in the Vale of Arryn. His nephew and heir Elbert Arryn was among those killed by the Mad King, sparking Jon Arryn's decision to join the rebellion.

Behind the scenes
Originally it was intended that Jon Arryn's death in King's Landing would open the series, following the depiction of the book's prologue, and the event would be discussed by Grand Maester Pycelle and Queen Cersei Lannister in a new scene not in the books. In the event this scene was not filmed for the pilot episode in favour of maintaining the opening from the novel.