The invitation from chancellor-elect Gerhard Schr�der to negotiate a coalition government is a decisive victory for one of Germany's most popular politicians - Joschka Fischer.

And the charismatic parliamentary leader of the German Green party sees the invitation as the most important result of the election.

"I think this is very decisive and it will change the party system, it will change the political system very positively," he said.

It has been a remarkable comeback for the Greens, who failed to get into parliament at all after unification in 1990.

And Germany's political transformation compares with Joschka Fischer's physical transformation - from overweight bon viveur to tee-total ascetic in two years - brought about by the collapse of his marriage, according to the German media.

No more "loony fringe"

Mr Fischer, a former taxi driver who now campaigns against motor vehicle pollution has made an equally large jump in strategic terms, from radical activist to Green pragmatist tipped to be Germany's next foreign minister.

Earlier this year, he said he was opposed to resolutions by party colleagues calling for a ban on the military and the withdrawal of Germany from Nato - ideas which Mr Fischer feared would cost his party the 5% of the vote necessary to win a seat in parliament.

During the campaigning, Mr Fischer shouted himself hoarse, trying to reassure voters that the "loony fringe" days of the Greens were long since gone.

Mr Fischer is able to put across the Green party line in terms of unassailable common sense.

When a BBC journalist questioned his party's promise of a 100kmh speed limit on the German autobahns, he replied: "What is the speed limit in the UK - 110? That could be a compromise. A good compromise."

His efforts paid off: The Greens succeeded in gaining more than 6% of the vote, and enough respect from the Social Democrats to be invited to talk about joining the government.

Unemployment a key issue

Mr Fischer will have to work hard to make his party fit to govern. As he prepares to start negotiations with the SPD, he is stressing issues on which the parties can happily work together.

"The biggest issue is: We have to fight against unemployment," Mr Fischer told the BBC. "And we think that we have in our programme a lot of proposals for negotiation."

The shrewd negotiator belies a character who has persistently defied convention.

Joschka Fischer's language in the German parliament, which he first entered in 1983, has at times been somewhat unparliamentary. One of his first speeches - in which he called the President an ass - has gone down in history.

Even his dress sense is a bone of contention. When he became environment minister in one of Germany's federal states, he was much maligned for going about his ministerial duties wearing trainers.

Whether he will invite as much disapproval in his new role remains to be seen - but Mr Fischer is clearly ready for the fray - and clear on the priorities for the new government.