Conventional isn't a word you'd apply to John Key.

Ever since coming into Parliament in 2002, at a time when National had just suffered its biggest ever drubbing at the election, he's broken the mould.

Three years after cutting his teeth and watching classmate Don Brash almost knocking Helen Clark off her perch, he decided to run for the leadership, even before a vacancy had been declared.

He won and finally did the job in 2008, inheriting Labour's newly signed free trade agreement with China which helped him handle the global financial crisis.

As leaders go he was unconventional, taking part in radio interviews that had us all cringing, posing for selfies with all and sundry, mincing along catwalks, falling of a stage and breaking his arm, being roughed up at Waitangi, fending off the ruffians with his cast, and generally telling us more than we ever wanted to know without even asking.

All these antics and his self-deprecating sense of humour endeared him to the public like no other, with the party he led rarely falling much below a support rating of 50 percent, unprecedented in the modern era.

John Key generally was an open book, but on his own future the book was firmly closed.  He only let on to his deputy Bill English in September - on his return from the leaders' week at the United Nations - that he was thinking of calling it a day.

However, he said nothing more of it until that day arrived, giving his colleagues just a week to find his successor.

The only other Prime Minister to voluntarily quit in office in recent times was the larger than life David Lange, whose personal life was in turmoil. He was forever making light of the serious business of politics, even telling a journalist on his sickbed that he was going to resign the following day. The journalist thought he was joking, and Lange had the last laugh when he did in fact step down the next day. 

For the jocular Key, his decision was no laughing matter. For this former money market trader it was pure business.  It's better to have a transition at a time of strength, he mused, not at a time of weakness which would be handing his successor a hospital pass.

Yeah, well National will now spent the Christmas break in intensive care, whether they graduate from life support will depend on how well they manage the process and who they choose to throw their weight behind.

Winning that elusive fourth term in office though has just become so much harder.