Helmut Kohl, who has died aged 87, will be remembered for his pivotal role in two extraordinary events: the fall of the Berlin wall and the rise of the euro. He devoted his entire adult life to Christian Democratic Union (CDU) politics and was Germany’s longest-serving chancellor of the 20th century.

Superficially, sheer physical bulk apart, Kohl bore unlikely comparisons with Otto von Bismarck. The aristocrat who unified a proliferation of states in 1871 and made Germany mainland Europe’s most important power was a Prussian Protestant of overwhelming intellect and resources who treated Europe like his personal box of building bricks. Kohl was a Roman Catholic Rhinelander, devoted as much to unifying Europe as to placing a united Germany at its head and heart.

His doctorate (on post-1945 Rhineland politics) was early evidence of an intelligence often masked by a thick skin, a dour impassivity, tactlessness and an apparently invincible optimism. His favourite tactic in a crisis was to sit tight and do nothing, to the despair of friends and the fury of opponents, in the usually justified belief that the trouble would go away. The image of the stolid, bloated monolith with the stentorian voice, the cartoon German with no sense of irony and a huge appetite was, however, grotesquely at odds with his political record.

Kohl was born at Ludwigshafen in the Palatinate, the son of Hans Kohl, a middle-ranking tax official, and his wife, Cäcilie (nee Schnur). He joined the Hitler Youth, like nearly all male contemporaries, including Pope Benedict XVI. The young Helmut soon shot up to 6ft 6in. Never one to forget a favour, or a grudge, he recalled postwar food handouts from American soldiers with rare affection and always had a soft spot for the US, although he never mastered English.

Early photographs show a handsome young man with an attractive smile and a shock of dark hair. As he began to put on weight, he became known as “the black giant” – as much a reference to the CDU’s party colour as to his own swarthiness. After studies at Frankfurt and Heidelberg universities, Kohl was elected to the Palatinate parliament in 1959.

By 1969 he was presiding minister. The federal CDU surprised everybody by making him its candidate for chancellor in the 1976 national election, even though he had been federal party chairman for only three years. He took on perhaps the most gifted politician produced by Germany in the 20th century: Helmut Schmidt of the Social Democrats (SPD).

The shambling, provincial booby faced the brilliant hatchetman from Hamburg. Nobody gave the black giant a chance against “Schmidt the Lip”. It was hard to wring even a vestige of light relief from Kohl, whereas Schmidt paraded his wit, dazzling everyone with his mastery of economics and world affairs.

Schmidt duly wiped the floor with his dull opponent intellectually, and Kohl became the butt of sometimes cruel satire. But on the night, his CDU/CSU alliance got 48.6% of the national turnout, becoming the largest single party in the Bundestag. Only Kohl’s political idol, Konrad Adenauer (CDU), the first West German chancellor, had done better.

Thanks to his coalition with the liberal Free Democratic party (FDP), Schmidt retained a tiny majority. Kohl became leader of the opposition in the Bundestag, but Schmidt’s brilliance saw to it that Kohl’s strong achievement at the ballot box was offset by his lacklustre parliamentary efforts. Once again he was the butt of satire, nicknamed “the Pear” for his girth.

His life’s ambition to become chancellor – embarrassing to sophisticated observers because of his lack of visible talent – suffered a setback when the next campaign began in 1980. Kohl was impatiently pushed aside by Franz Josef Strauss, the rightwing leader of the CDU’s Bavarian sister party, the CSU, who alone could match Schmidt in intellect and wit. But Strauss was erratic and unsteady under fire. Schmidt thrashed him, too, and led his SPD-FDP coalition into its fourth successive term, with a bigger Bundestag majority. Kohl trudged on as opposition leader in Bonn, even more underestimated than before.

As its chairman, he devoted much of his time to mastering the CDU party machine, winning the support of activists at all levels and earning exceptional personal loyalty. This was one of the secrets of his remarkable success and longevity in politics and office alike, which were eventually to surpass even Adenauer’s, whom he matched in 1994 with a fourth general election triumph (one more than Margaret Thatcher, whom he admired but heartily disliked).

In 1990, on the crest of the unification wave, he had won the CDU/CSU a record 48.8% share of the vote. His other assets included energy and stamina. In keeping with his enormous bulk, Kohl had what the Germans bluntly and appropriately call Sitzfleisch (staying power), literally the flesh on which to outsit everyone else. He could also stump the country from dawn to midnight, delivering crushing speeches that started at maximum volume and stayed there.

After a hard day’s politicking, something he loved in all its forms, he would sit down with his kitchen cabinet and eat a huge helping of belly of pork, a quintessentially German peasant dish and his favourite. The cronies of those days say that this was when he came into his own as a convivial companion, free to shed the German convention that inhibited even Schmidt – that politicians must be solemn if they wish to be taken seriously.

Whereas in private it could be over-whelmingly genuine, his bonhomie in public seemed less real than the occasional flash of rage at protesters. Hit by an egg in Halle, Saxony-Anhalt, in 1991, Kohl crashed into the crowd to confront the single offender with the roar: “You’re a rabble!” Here was passion at last from the father of the fatherland of which he so often spoke sentimentally. It was also a vintage Kohl story, complete with infelicitous choice of word.

Stamina, however, was one of his hallmarks. He would go to a health farm in Austria every summer and shed two stone in three weeks, a potentially dangerous undertaking, but the weight was just as rapidly regained. The stamina seldom flagged, even when everything was running against him and he neither took action nor produced any stratagem to save himself, except to sit tight. Reports of his political demise were exaggerated for more than 20 years. It is difficult to think of a politician so consistently underrated.

Kohl’s vengeful satisfaction knew no bounds in October 1982 when Schmidt, the man who had mocked him for years, fell out on economic policy with the FDP, which crossed the floor to present the CDU with a Bundestag majority – and Kohl with the chancellorship. As the Guardian said at the time, a great man made way for a large one.

The blunders and fiascos soon mounted. Two of his ministers were embroiled in corruption scandals. Kohl went to Israel and infuriated his hosts by presenting himself as leader of the new majority of Germans who had nothing to do with the past. The subtext was that they were not going to be pushed around by emotional blackmail. The visit was a diplomatic disaster.

So was President Ronald Reagan’s trip to West Germany in 1985 for the 40th anniversary of the Nazi surrender, when an insensitive Kohl sent him to lay a wreath at a cemetery where Waffen-SS men lay among the buried. Kohl’s remedial afterthought was to take Reagan to Belsen, thus digging himself even more deeply into the hole of his own lack of tact. Nor could he understand why he was left out of allied celebrations of the big anniversaries of D-day and of the end of the war. The point that Germany had been the villain of the piece seemed to be lost on him.

These were stupefying blindspots for a postwar chancellor, who nonetheless eventually learned to condemn “crimes committed in the German name”, even though he seemed unable to grasp that they had been done by Germans, albeit long dead, rather than aliens. Ironically, the East German regime held exactly the same view, a rare demonstration before 1990 of German unity. Yet his determination that no war would ever again be unleashed from German soil was unquestionably genuine, and he insisted, against his mother’s pleas, on naming his two sons respectively after his uncle, her brother, killed in the first world war, and his own elder brother, killed in the second.

Kohl’s early difficulties in office often resulted from reluctance to do his homework. He was always ready to stay up half the night, convivially talking politics and persuading people behind the scenes, but the German bureaucracy’s briefings on every conceivable eventuality (except, quite often, the one that actually happened) left him cold.

But in time, he found the right people to whom to delegate such chores. Banana skins proliferated but the thick-skinned Kohl refused to fall over. Here was another component of his success: a master of machine politics, Kohl also knew what ordinary Germans felt and wanted. He managed always to be seen to be on their side; the ordinary chap, the intellectual underdog who made mistakes like everybody else but doggedly hung on while lefties and media sophisticates mocked.

It was an extraordinary act. The man who dominated the state got away for years with presenting himself as its principal opponent. Like Thatcher and Reagan, the contemporaries he outlasted, he presented himself as “against the government” even as he led it. Unlike them, he knew when to stop, never questioning the social market economy, the moderate consensus among big business, liberalism and social democracy that lay behind West German postwar success. He cultivated his provincial, anti-intellectual image with care – and usually had the last laugh, as he did with Schmidt. He loved being in the chair at cabinet, even when those around him were in disarray and waiting for a lead that did not come. He would merely urge people to agree so they could all go home.

Home in the Palatinate was where his wife since 1960, Hannelore Renner, mother of the two sons and looking the very model of a German countrywoman, spent most of her time while her husband got on with the business of government in Bonn. Just as they had glossed over the incorrigible philandering of the SPD chancellor Willy Brandt, Schmidt’s predecessor, the not always benevolent West German media drew a veil over Kohl’s longstanding relationship with a woman on his personal staff in Bonn. The liaison even survived the moralising calls for a return to family values – part of his first campaign as incumbent – making him the secret envy of many an Anglo-Saxon politician. Like the French, the Germans – down-to-earth and unpuritanical – saw no hypocrisy in such private arrangements.

Having become chancellor through a constitutional coup, Kohl felt vindicated and legitimised by the first of his four successive election victories in March 1983. The SPD’s prolonged inability until 1998 to produce a real challenger (and the elimination of any likely rival in the CDU) helped to turn him from a joke into a monument. Under him, Brandt’s famous remark – that (West) Germany was an economic giant but a political pygmy – ceased to be true, as German troops turned out for Nato and the UN.

Luck played a role in the spectacular rise of Kohl. There was Schmidt’s virtual political suicide, which gave him the chancellorship; and there was the Soviet Union’s implosion at the peak of his career. Kohl’s hatred of communism did not prevent him from doing business with Mikhail Gorbachev. The chancellor relied totally on his political instinct in making the moves that led to the fall of the Berlin wall in 1989 and reunification within a year. “We all felt as if we were taking part in a dream,” said one of his intimates. The cartoonists’ blundering buffoon knew he had to get Gorbachev’s signature on as many pieces of paper as possible – while stocks lasted.

Unfazed by the Russian leader’s intellectual superiority, Kohl knew he faced a man whose days were numbered. He probably knew it before Gorbachev himself. The politics and even the diplomacy worked like a charm, and the world was stunned when Gorbachev pulled the rug from under the East German regime of Erich Honecker. The last Soviet leader made it clear he would not help to crush mounting East German civil disobedience, which led to the panicky decision to open the wall in November 1989. With unflagging energy, Kohl pursued the complex settlement that led to reunification on 3 October 1990.

The wheeling and dealing with Gorbachev was his moment in history, and he made the most of it. But the blunder factor never quite went away. The economic side of reunification was a shambles. With an election coming, Kohl not only refused to raise taxes to pay the huge bill; he promised that there would be no extra taxes at all and that nobody would suffer as a result of union. The first colossal instalment for regenerating the economy in the east was therefore borrowed, which meant that taxpayers (after the 1990 election, which Kohl won with a record majority) had to pay interest as well as the capital while the new, united Germany plunged into unprecedented debt.

But the chancellor’s luck did not yet desert him. Within four years, the east began to come right. Neo-nazi nastiness notwithstanding, the east Germans were not destabilised by unemployment of up to 40%, free-market forces, western patronising and ruthless carpetbagging. Consumption and construction boomed as Kohl prepared to shift the government from sleepy, westerly, Rhineside Bonn to bracing, ex-Prussian, east-facing Berlin in time for the new millennium.

With reunification achieved, the next item on his agenda was to re-energise and strengthen the European Union. During his long watch, the EU had expanded to 15 states. Even Thatcher’s Britain had adopted the Single European Act and the Maastricht treaty, foreshadowing monetary union, had been agreed.

The EU, already augmented by the former East Germany, was poised to admit new members from further east while Kohl worked tirelessly, with the French above all, towards the creation of a European central bank in Frankfurt as midwife for the euro, on the model of the Bundesbank which had so successfully nurtured the deutschmark.

If Kohl had vision, it surely lay here: he knew that he was upsetting the German conservative majority with its folk memories of currency catastrophes in 1923 and 1945 in preparing to ditch the sacred deutschmark in the name of an increasingly unpopular mission, but ploughed on regardless. For the prize of currency union, he tolerated very high unemployment, accompanied by outbursts of sometimes violent xenophobia and neo-fascism as well as high taxes, while pouring money into the bottomless east German pit.

He worked tirelessly with such disparate and often uneasy French colleagues as presidents François Mitterrand and Jacques Chirac on the great Euro-project and on the German-French partnership, which remains the core of the EU, symbolised by such pet initiatives as the Franco-German integrated army brigade and the Arte bilingual television channel. We are left with the faintly ridiculous but also touching photograph, taken from behind, of the mountainous Kohl and the diminutive Mitterrand side by side, holding hands at a remembrance ceremony on the battlefield of Verdun. His sensitivity in handling a prickly western neighbour was not matched by his tactless treatment of a no less prickly Poland, whose tenure of what was before 1945 German territory he took far too long to accept. But accept it he did.

Yet by the time the euro was launched at the beginning of 1999, Kohl was out of office. The SPD was back in the shape of Gerhard Schröder, who trounced an exhausted Kohl at the federal election in September 1998. Kohl led the CDU to its worst defeat, even losing in his own constituency of Ludwigshafen (he was also top of his party’s list of candidates in the dual ballot and therefore kept his Bundestag seat until he retired in 2002).

Within a year of his defeat, he was up to his ears in a vast CDU funding scandal involving alleged kickbacks from the sale of German tanks to Saudi Arabia, deposits of more than 300m deutschmarks in Swiss banks and a dubious deal whereby French oil interests got control of more than 2,000 state-owned petrol stations in the former East Germany in exchange for investment in the dilapidated chemical industry there (and more alleged secret subventions to the CDU). The seemingly interminable Bundestag inquiry appeared incapable well into the 21st century of coming to a conclusion.

Hannelore, his estranged wife, suffered from photodermatitis, a rare condition that forced her to live in the dark to protect her hypersensitive skin from daylight. She took her own life in 2001.

Kohl appealed successfully to the courts for the suppression of his Stasi file, the undoubtedly fat dossier assembled by the spies and informers of the insatiable East German ministry for state security. Inevitably, observers wondered what embarrassments it might contain as lesser Stasi targets, east and west, had to endure painful exposures of their secrets and betrayals. Even so Kohl enjoyed a rehabilitation of sorts and was invited for coffee and cakes by the next CDU chancellor, Angela Merkel.

After his retirement from politics Kohl lived quietly, but not without drama. In December 2004, a Sri Lankan air force helicopter rescued him from a hotel where he had been stranded by the tsunami in the Indian ocean. And in April 2008, he suffered a bad fall and was taken into intensive care, unable to speak. But he made a remarkable recovery and was married for the second time that May to his partner of some years, Maike Richter, then aged 43.

She became fiercely protective of the ailing statesman, who underwent major operations in 2010 and 2012 and latterly relied on a wheelchair. His speech was permanently impaired by the stroke that accompanied the 2008 fall. His wife took control of his correspondence and archives, writing letters for him and denying most people, including old friends and colleagues, access to him. This led to the estrangement of his sons, Walter and Peter, who gave indignant interviews to the German press.

In his later years Kohl gave interviews in which he criticised his successor and erstwhile protegee Merkel for her austerity policies in the euro crisis and for not standing up strongly to the Russian president Vladimir Putin over his conduct towards Ukraine.

Earlier this year Kohl won record damages of €1m from the Random House publishing group for an unauthorised biography that allegedly breached his right to privacy by assembling a mass of comments from a series of interviews the former chancellor had given over a period about a decade earlier.

Kohl may have been as different from Bismarck as Bonn is from Berlin, but he was just as much of an iron chancellor, iron in endurance, unshakable in his self-confidence. The author of several books, including memoirs, the man once mocked as Helmut II for being so much duller than Schmidt’s Helmut I, will have his revenge in the history books too. It was Kohl, not Schmidt, who stood ready when the bandwagon of German reunion came by. In his paradoxical, bumbling way, he proved in the end to be great as well as large – and lucky with it.

He is survived by Maike and his sons.

• Helmut Josef Michael Kohl, politician, born 3 April 1930; died 16 June 2017