Wikipedia:

Lipponen first came into the political limelight when he was secretary to the then Prime Minister Mauno Koivisto from 1979 to 1982. Frequently having to substitute for the busy PM, Lipponen was soon dubbed vara-Manu ("deputy Manu" -- Manu being short for Mauno).
Lipponen was a Member of the Parliament of Finland from 1983-1987 and also from 1991 until he retired in 2007. In 1993 SDP chairman Ulf Sundqvist was suspected and later convicted of a large financial fraud. Lipponen was elected the new chairman in 1993, and he led the party to victory in the parliamentary election of 1995. Lipponen formed a cabinet of five parties including both rightist and leftist parties. Lipponen's economic policies were however dominated by the right-wing. The main task of the cabinet was to decrease the number of unemployed. Lipponen was one of the EU's visionaries and tight fiscal policies allowed participation in the European Monetary Union, which resulted in the introduction of the Euro in 1999. Foreign trade increased above the European average 1995-1999. Laws for a new constitution were passed and it took effect on March 1, 2000.
Lipponen headed the SDP campaign in 1999, which resulted in losses, but the SDP remained the largest party in the parliament. The coalition formed in 1995 was renewed. During the second Lipponen cabinet, Lipponen headed Finland's six months in the EU presidency and led pro-integration and pro-expansion policies. Lipponen introduced the concept of a European constitution during a speech in Bruges in 2000.

In the national election campaign of 2003, Lipponen was defeated partly by the disturbing run up to the Iraq War that paralleled the campaigns of all parties. There was a majority public sentiment against the Iraq War, and a reliance on the UN to prevent it. Hans Blix was well known to the Finns, and trusted.

During the Iraq disarmament crisis before the 2003 invasion of Iraq, Blix was called back from retirement by UN Secretary General Kofi Annan to lead United Nations Monitoring, Verification and Inspection Commission in charge of monitoring Iraq. Kofi Annan originally recommended Rolf Ekéus, who worked with UNSCOM in the past, but both Russia and France vetoed his appointment. Newt Gingrich stated that approving Blix as chief UN weapons inspector was one of the biggest mistakes the United States ever made.

Lipponen's main opponent in the election, was Center Party chairman, Anneli Jäätteenmäki.

Anneli Jäätteenmäki resigned on June 18, 2003, under pressure resulting from the accusation that she had lied to Parliament and the public over how she had acquired confidential Foreign Ministry documents which she used for political purposes during the election campaign. The documents contained diplomatic information from a meeting between United States President George W. Bush and Prime Minister Paavo Lipponen about Finland's position regarding the Iraq war. Jäätteenmäki used the information to suggest that her rival, the Social Democrat leader Paavo Lipponen, had secretly offered Finnish support for the U.S.-led coalition, a substantial breach against the official policy of neutrality in Finland's foreign politics, and thus associated Finland with what many Finns considered an illegal war of aggression.

Jäätteenmäki broke the traditional unity and silence behind Finland's security policies. As the elections turned out to be close, the defeated Social Democrats found reasons to suspect that her non-traditional campaign was decisive for the outcome, which soured the relationship between the two major coalition partners.

I believe that Lipponen was continuing the powerful traditional Paasikivi-Kekkonen Line of active neutrality. In practice, this was an extension of the strategies developed before and during WWII for the survival of a small independent country as a no-man's-land between Germany and the Soviet Union, and later developed to handle a similar position post-war between the Soviets and Nato.

The Paasikivi-Kekkonen Line is a poker game strategy. Socialize, psyche your opponents, count the points, be modest, bet when you're sure, but suck your opponent in. Above all, don't make a fuss. It's backroom stuff, not grand-standing. More diplomacy than politics.

Whatever Lipponen said to Bush in private, and to the world in public, they were part of a longer term plan to remain actively neutral, and a shorter term plan to give Blix more time and prevent war. With Russia as a neighbour, this would be the obvious stance.

This however is a personal interpretation. We shan't see the papers for 50 years, and even then, I doubt if it there will be a dénouement.

Now some of the bad stuff. Wikiedia again:

On August 15 2008, during the Russian response to the Georgian invasion of South Ossetia, Nord Stream, a Russian gas project, announced that it had signed a consulting contract with Lipponen. According to Nord Stream, he advises on the Environmental Impact Assessment (EIA) and permit applications in Finland. He provides independent consultations according to his expertise in Finnish administrative and decision-making procedures within the energy sector.
As a result of the scandal that followed, Lipponen relinquished his office in the parliament building and resigned from all of his duties in Finland except veteran activities.
In an article published in October 2008 Lipponen discussed the Russian response in Georgia and warned Europe of its dependence on Russian gas. Lipponen criticised the way many Finnish and German politicians are opposed to nuclear power and stated that their fundamentalism destroys both energy security and climate policy.
Poland reportedly blocked Lipponen's candidacy as EU foreign policy chief because of Lipponen's ties to Nord Stream.

This sorry episode may show Lipponen returning to his socialist origins. He certainly still has good contacts with Russia. Or it maybe is a man looking to make some money for his old age - I don't think he has profited, before this episode, from government business - certainly not visibly.
Lipponen speaks excellent English, but he's a slow and deliberate speaker with a certain tough charisma, but no sparkling soundbites. WYSIWYG. But he appears to be a good organizer, a dogged negotiator and not afraid to bang heads together when required. If he were to become President of the European Council, he would be fairly invisible, but the work of the so called `Summit meetings' of the EU, of the member heads of state, would be much improved imho.

Lipponen is not a unique candidate for the post - but he is one of them. I hope this profile may contribute to a better analysis of the post and who should fill it when Lisbon is signed.