Hand of the King

The Hand of the King or King's Hand is the most powerful appointed position in the Seven Kingdoms, second only to the King on the Iron Throne in authority and responsibility. It may be comparable to the role of a prime minister in an absolute monarchy. The Hand is the King's closest advisor, appointed and authorised to take decisions in the King's name.

In the books
In the Song of Ice and Fire novels, the events of the story are set in motion by the death of the Hand of the King, Lord Jon Arryn, apparently from natural causes. King Robert Baratheon travels to Winterfell and asks Lord Eddard Stark to replace Jon. Eddard is doubtful, not wishing to travel far from his homeland and his family, but eventually agrees when an anonymous message claims that Jon Arryn was murdered. Eddard decides to agree to the King's offer so he can investigate and determine the truth of what has happened and if it poses a danger to Robert or the realm.