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Many prime ministers in New Zealand have either been shuffled from power by a rival, such as Jim Bolger, or lost an election and had their legacy tarnished, such as the late Sir Robert Muldoon.
Former Labour leader Helen Clark lost a fourth attempt to hold her job as prime minister and left a leadership void which so far, Labour has been unable to fill successfully.
Mr Key has decided eight years as prime minister, and 10 years as National Party leader, is enough and he will leave the job next Monday and Parliament at the end of the current term. His resignation will not trigger an expensive by-election.
Mr Key was a stabilising influence in world politics as conservative leaders changed in Australia, Canada and Great Britain. Mr Key was enduring and his view of politics allowed him to think on a different level than most other politicians, several of whom have made politics their career.
When Mr Key became National Party leader, the party had just failed to get into power under the leadership of Don Brash. Dr Brash played the race card and nearly won, something which would have meant putting New Zealand on the edge of racial disharmony.
For his part, Mr Key has advanced race relations and injected momentum into the Treaty of Waitangi settlement process. After saying he would not attend Waitangi Day events in Waitangi next year without being able to speak, the organisers agreed to his terms. The next leader of National will need to carefully consider his or her intentions on race relations and Treaty settlements.
The Key family has also been at the centre of media attention since Mr Key was elected to office. He said his career as a politician had left his wife Bronagh with many nights and weekends alone and his success as a politician had come at quite the sacrifice of his family, the people dearest to him. His daughter Stephie and son Max had grown up in public, not an easy thing to do when your father is a high-profile politician in a small country.
Mr Key entered politics by challenging a non-performing MP in Helensville, won the challenge and went on to make a strong statement about his future. Independently wealthy, Mr Key could afford to be daring in his political leadership - some of which did not always find favour with all sectors of society.
However, Mr Key was seen as a real Kiwi, someone to have a beer with at a barbecue, someone to watch rugby with, someone on first name terms with the All Blacks, but also someone who played golf in Hawaii with the most powerful man in the world - United States President Barack Obama.
His humble beginnings in a Christchurch state house were also part of who he was but he became a wealthy currency dealer through determination and steel - a quality which he took with him into political life.
The legacy Mr Key will leave is one of financial stability, a unified government, a record of strong economic management and a commitment to lift as many New Zealanders out of poverty as possible. A shortage of suitable housing has been laid at the door of Mr Key but his efforts in trying to sort out that particularly difficult area have been assiduous.
One of the issues he received the most criticism for is failing to bring home the bodies of the Pike River miners who died in the explosion. While Mr Key would have meant what he said at the time, the pragmatism which ruled his career meant he made a tough call to allow the mine to be sealed. Then there was the failed flag referendum.
But, his leadership during the Christchurch, and latterly Kaikoura, earthquakes was seen as outstanding by most New Zealanders. New Zealand secured a seat on the United Nations Security Council in no small part due to the work carried out by Mr Key.
The National Party caucus, like the rest of the country, have been stunned by the announcement. In a week, National MPs have to decide on a new leader and prime minister to lead them into the next election.
For the sake of the country - in a time of global uncertainty - it is hoped Mr Key has been planning for succession.