BERLIN (Reuters) - Peter Altmaier once said he would never rise to the top tier of German politics because of his appearance -- he is a huge man who seems perpetually dishevelled, with shirt untucked and tie askew.

FILE PHOTO: German Chancellery minister Peter Altmaier attends the weekly cabinet meeting at the Chancellery in Berlin, Germany, September 27, 2017. REUTERS/Fabrizio Bensch/File Photo

But Chancellor Angela Merkel’s chief of staff and stand-in finance chief could become the most influential minister in her next coalition government, senior officials say.

In recent years, Merkel has often turned to Altmaier, who is known as her “Allzweckwaffe” (all purpose weapon), to carry out the most sensitive and complex tasks, from securing majorities for unpopular Greek bailouts to coordinating the government’s response to the 2015 refugee crisis.

Since a Sept. 24 election, he has also emerged as a bridge builder between the disparate parties in coalition talks.

If the talks succeed, some officials believe Merkel will try to keep him at the finance ministry so he can tackle what may be the biggest challenge of her fourth term: brokering a deal with French President Emmanuel Macron on a reform of the European Union.

“If Merkel made him finance minister for this transition period, then it is a sign that she trusts him to do this job in the future,” a senior aide to the chancellor told Reuters.

Henrik Enderlein, head of the Delors Institut in Berlin, a think tank, said it would send a “very strong signal” to France if Altmaier continued in the finance ministry post.

The liberal Free Democrats (FDP) are expected to have first choice of ministry in the new government. But if their leader Christian Lindner does not claim the finance ministry for himself, Altmaier could be in pole position.

Although the FDP and members of Merkel’s Christian Democrats (CDU) are skeptical about some of Macron’s proposals - notably his idea to create a budget and finance minister for the euro zone - some believe Altmaier’s tone alone would inject new momentum into the relationship between Berlin and Paris.

Altmaier, who declined to speak to Reuters for this story, has not said publicly whether he is interested in becoming finance minister permanently

After meeting French Finance Minister Bruno Le Maire last week, he said not all proposals from Paris would be greeted with “unlimited enthusiasm”. But he added: “I never made it a secret that I’m an advocate of Franco-German cooperation.”

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EXTRAVAGANT DINNERS

A jovial 59-year-old from the state of Saarland on the French border, Altmaier stands out among politicians and the officials in Merkel’s close entourage, dominated by technocrats.

The son of a coal miner and a nurse, Altmaier was the first prominent German politician to actively embrace Twitter.

He hosts extravagant dinners at his vast apartment in west Berlin, cooking “Gefilde” -- a Saarland specialty of potato dumplings filled with liverwurst and soaked in a bacon-cream sauce -- for guests of all political stripes.

Altmaier speaks fluent English, French and Dutch and, unlike his boss, is a master communicator.

He also likes to make fun of himself, particularly his weight, which he estimated several years ago at 140 kilos (309 pounds) but now describes as a “state secret”.

“I may not be the ‘wichtigste’ (most important) minister but I am the ‘gewichtigste’ (heaviest),” he has joked.

DARK HORSE

After years as Merkel’s “Mr Fix It”, some CDU officials see him as a dark horse candidate to succeed the chancellor one day.

As parliamentary whip for the CDU, he won over skeptics about the Greek bailouts with home-cooked meals and red wine.

“The thinner the majority, the fatter Altmaier gets,” Bundestag members used to quip.

Later, as Merkel’s environment minister, he brought order to her nuclear power phase-out and was appointed her chief of staff in 2013. Two years later, she turned to Altmaier for help over the arrival of hundreds of thousands of refugees and again this year to write the CDU’s election program.

In coalition talks between Merkel’s conservatives, the FDP and Greens, Altmaier has been a mediator, gently nudging the parties closer together, participants say.

Like Merkel, he is a CDU moderate. After joining the Bundestag in 1994, he incurred the wrath of traditionalists by pushing for a reform of strict German citizenship laws and the rehabilitation of World War Two deserters.

He was part of the “Pizza Connection”, a group of young lawmakers from the CDU and Greens who met regularly at an Italian restaurant in Bonn, when the environmentalist party was viewed as a radical, fringe group by many conservatives.

Before entering German politics, Altmaier studied European law and worked at the European Commission, later participating in the European Convention that led to the EU’s Lisbon Treaty.

“Altmaier is one of a small number of top-tier German politicians who has real experience in Brussels,” said Martin Selmayr, chief of staff to European Commission President Jean-Claude Juncker, who worked with Altmaier in the Convention in 2002.

“He is a committed European and would be a powerful pro-European voice in any German government.”