Key Points:

Michael Cullen has followed Helen Clark's example and resigned as Deputy Leader of the Labour Party.

Helen Clark announced her resignation as leader after Labour failed to win back power last night.

In a statement announcing his own decision to stand down today, Dr Cullen said it was "time to move on from a leadership position as the party rebuilds".

He wished his National counterpart Bill English well as minister of finance and said he looked forward to seeing National deliver on its promises.

"Labour will measure National in government against the commitments it has made and I will play my part in holding the National-led government to account as Labour rebuilds and prepares for the next General Election," Dr Cullen said.

Where to now for Helen Clark?

Helen Clark has never admitted to having a Plan B. But it's hard to believe someone whose managerial prowess at navigating through the contortions of MMP would not have a back-up strategy if last night's trend to a National victory was confirmed.

Friends and associates say a role on the international stage would be hers for the taking, given her high standing overseas _ perhaps a United Nations post, definitely the lecture circuit.

Left-wing media commentator Russell Brown wonders if her softened, pink-jacketed turn in the final TV leaders' debate was, in part, the first step in moving on. "Because people do want to be well-remembered."

He predicts her exit, like everything else in her career, will be managed in an orderly fashion. "There's nothing in it for her being dragged out of office."

Brown's best guess timeline: six months to allow her successor to stake his claim. Phil Goff and David Cunliffe are being talked about.

One of the few times Clark publicly touched on her departure was in a 2003 North & South interview. "It's a fine judgement, when to exit," she said. "You feel like if you've got the energy, and it does require an enormous amount of energy and motivation ... you'll keep standing there. And getting results means needing to enjoy the confidence of your colleagues and the confidence of the public. When those factors start to change ... then you re-evaluate."

Getting results was a hallmark of Helen Clark's premiership. She was loved and hated for her methods. In her first term, she gained a reputation for dealing swiftly to those who threatened to tar her with their foolishness. Among the punished: Work and Income boss Christine Rankin, ministers Dover Samuels, Ruth Dyson and John Tamihere.

She was across everything. Some called it strong leadership. Firm, decisive, necessary. Opponents called it high-handed, ruthless, control-freakery. Minister for Everything, they taunted; welcome to Helengrad.

Her Government's programme of progressive social change _ civil unions, prostitution law reform, the Green-initiated repeal of the "reasonable force" defence to child assault _ fed an undercurrent of paranoia about "Auntie Helen", the omnipotent school prefect lecturing us in our own homes.

PC, she once said, is "shorthand for right-wing opponents attacking everything you do" _ too liberal, too conservative, there was no consistent rationale. Don Brash voted for the prostitution legislation; National supported the final version of the misnamed "anti-smacking" law.Says Bryan Gould, a former British Labour MP and vice-chancellor of Waikato: "There's something that gets under the skin of a certain section of the electorate when they see a successful woman coming at them from the left."

Not only successful, but cerebral, analytical, sensible, and tough. Her sneering one-liners didn't have the pomposity of Michael Cullen or the caustic bite of David Lange but they weren't particularly ladylike. And they were more memorable than her circumspect rhetoric.

From becoming leader of the Labour opposition in 1993 _ with an approval rating of 2 per cent _ there was a series of image make-overs designed to soften, to "humanise" and "feminise" Clark. Remember the glamorous 2005 campaign shot with the straightened teeth?

This year, in the one-man satirical philosophical play On the Conditions and Possibilities of Helen Clark Taking Me as Her Young Lover, an actor presented a Powerpoint lecture trying to convince us that Clark must take a lover to ensure her political survival and for the benefit of the country. It was probably the kindest speculation on Clark's sex life yet.

Scuttlebutt around her love life has trailed Clark through most of her 37-year political career. The lesbian rumours; the fact that she didn't want to marry out of her feminist convictions (she called it a "necessary evil" for her political career and cried on her wedding day); that she chose not to have children.

In broadcaster Brian Edwards' 2001 book on Clark, the Prime Minister's husband Peter Davis said of the marriage: "You were more or less ambushed into it. I didn't really mind. Helen is strong-willed and her whole life has required her to bend that will at certain times."

On the question of children, Clark told Edwards: "It was a very deliberate choice and I'll never regret it ... I don't think anybody could accuse me of being selfish. My whole life is so outwardly directed towards other people."

No regrets. No worrying in bed at night. Make your own luck. Clark has always kept her eye on the main prize. Pragmatism first. She was excoriated for this, especially from within the Left.

In his memoir, David Lange criticised her for not joining the Cabinet battles over Rogernomics. "She responded by putting her head down," he wrote. "She was by her own account a survivor: as long as her paddock had a good sole of grass the firestorm could consume the rest."

Later, Clark responded: "I was sitting at the bottom of the table. It was a bit like, the grass gets trampled when the elephants fight."

Clark hoped to be remembered for changing the paradigm so that Rogernomics could never happen again _ that is why Brash terrified her.

Her second term saw rifts open with the Greens after she lifted the moratorium on GE research following the "proceed with caution" message from the royal commission, despite popular opposition. First Labour turned away from the much-touted Closing the Gaps programme to lift Maori, and then the foreshore and seabed stoush triggered a 15,000-strong hikoi on Parliament.

That was after activist Titewhai Harawira brought Clark to tears on Waitangi Day 1998, then led her onto the marae the same day four years later.

Still, the economy was strong and the world was impressed, with Forbes Magazine ranking Clark the 20th most powerful woman in the world in 2006 (56th this year).

At home, a motley procession of "-gates" tugged at her credibility _ Doonegate (ill-advised dismissal of the former police commissioner), Paintergate ("forgery" of amateur art for charity), Speedgate (the 170km/h prime ministerial motorcade dash for a rugby match). She waved them away impatiently.

But when the dust clears, how will she be remembered? The Labourite daughter of a staunchly National farmer? The long-haired student protester turned cautious technocrat? The mountaineer and loyal friend? The natural diplomat who enabled New Zealand to punch above its weight? She would perhaps like to be remembered for her pursuit of an economically robust social democracy.

Politically, one of her biggest legacies will be dragging both National and Labour into the political centre. Gould said: "She'll be seen as someone who restored a sense of who we are ... She's given us back the choice of traditional New Zealand values."