Wolfgang Mommsen

A leading German historian, he brought academics together to further the understanding of his country's past
The historian Wolfgang Mommsen, who has died of a heart attack while bathing in the Baltic Sea at the age of 73, was a leading member of a remarkable generation of liberal and left-leaning historians who championed a more critical attitude to the German past from the 1960s onwards.

He came from a famous family of scholars: his great-grandfather was Theodor Mommsen, a leading late 19th-century liberal and winner of the Nobel Prize for Literature for his trilogy on the history of ancient Rome. Visitors to Wolfgang's family home in Düsseldorf, overlooking the Rhine, could not escape noticing the large gallery of photographs of the many eminent professors whom he numbered among his ancestors and relatives. His father, Wilhelm Mommsen, was also a historian.

So, too, was Wolfgang's identical twin brother Hans, whose career matched his with uncanny precision. After studying in Marburg, Wolfgang obtained his doctorate in Cologne in 1958, in the same year as his brother was awarded his PhD in Tübingen. Both were appointed to chairs in the same year, 1968: Hans in Bochum, Wolfgang a stone's throw away in Düsseldorf.

To attend a German historical conference where both were present was an uncanny experience, as each, in true professorial style, flitted from one parallel session to the next, making participants who did not know them wonder why the same historian had to make two different contributions to the same discussion within the space of a few minutes. Hans smoked and drank, while Wolfgang did not; and seeing them together was like seeing the effects of 40 years of alcohol and tobacco on the same body: Wolfgang was undoubtedly the leaner and fitter of the two, though even he perhaps was throwing caution to the winds when he plunged fatally into the cold waters of the Baltic.

While Hans eventually became an important historian of Nazi Germany, Wolfgang specialised in the Imperial period, from the middle of the 19th century to the end of the first world war. His dissertation, on Max Weber and German politics, published in English in 1984, must surely be one of the most brilliant debuts a historian has ever made: it revolutionised our understanding of the 20th century's most influential sociologist by setting him firmly in the context of his times, and showing him to be a liberal nationalist and imperialist, much to the horror of many of his admirers. He went on to demonstrate that a knowledge of Weber's political thought and action was essential if we were to grasp accurately his theory of power. This was an outstanding achievement, and Wolfgang followed it up by playing a leading role in editing a new, comprehensive edition of Weber's works; his dynamism was essential in pushing on towards its completion.

The Mommsens were related to Weber by marriage, so there was something particularly iconoclastic in Wolfgang's book, which caused a huge storm when it first appeared. Building on this, he went on to produce a wide range of studies on German liberalism and on imperialism. But in the central period of his career, it was as an academic politician and administrator that he made his mark. A spell as a British Council scholar in Leeds at the end of the 1950s had made him into something of an Anglophile: it was a mark of his acculturation that the best gift one could take him on a visit to Germany was a packet of plain English tea - Liptons, PG Tips or Brooke Bond, not the fancy concoctions that are all one can obtain in German grocery stores. So it seemed natural that he should take over as director of the recently founded German Historical Institute in London in 1977.

Wolfgang's energy quickly made the institute into the most important centre for British historians working on Germany. He raised large sums of money, building up a well-stocked library and moving the institute into spacious and elegant new premises on the corner of Great Russell Street and Bloomsbury Square. He attracted a brilliant generation of young German historians as research fellows. And above all, perhaps, he organised a string of important conferences, of which the most influential was held in 1979, on state and society in Nazi Germany. The vehemence of the clashes between those who argued that it all came down to Hitler, and those who argued for the primacy of structural forces, took many observers aback, and still reverberates today.

In such a setting, Wolfgang was in his element. His love of controversy found another outlet in his cogent contributions to the debate that raged in Germany in the mid-1980s over whether the time had come to draw a line under the Nazi past: Wolfgang was sharply critical of those, such as the rightwing historian Ernst Nolte, who thought it had. All of this was too much for the conservative government led by Helmut Kohl that came to power in West Germany in 1982, however, and Wolfgang was effectively forced to return to his chair in Düsseldorf in 1985, leaving the institute in less energetic hands.

Wolfgang quickly found another role as president of the Association of German Historians from 1988 to 1992, and in this capacity took a lead in arguing against those who saw German reunification as the opportunity for a more nationalist view of the German past. In the mid-1990s he produced his masterwork, a huge, two-volume history of Germany from 1850 to 1918, elegantly written, comprehensive, and full of stimulating insights and material scarcely known even to specialists. On their simultaneous retirement in 1996, the Mommsen twins spoke jointly at a seminars in London and Cambridge: their mutual competitiveness had not diminished with time, and it was almost impossible for other participants to get a word in edgeways as each launched into a string of criticisms of the other's paper.

Wolfgang was not always an easy character to work with; he could seem arrogant and self-important, though those who knew him well could see through these traditional social attributes of the German professor to the real man underneath. He was particularly kind to younger British historians, and made those of us who knew him feel that we were making an important contribution to explaining his country's past, whether we really were or not. His infectious, braying laughter enlivened many an academic occasion and revealed a lighter side to his nature.

His perpetual restlessness and youthful energy led him, in his 60s, after his children had grown up and left home, to leave his wife for a graduate student. However, the relationship did not last, and Wolfgang spent his final years in a bachelor apartment in Berlin, continuing to work on the Weber edition and to publish books, the most notable of which was a study of Germany's part in the origins of the first world war. He is survived by his wife Sabine and their four children.

· Wolfgang Mommsen, historian, born November 5 1930; died August 11 2004