Born into a middle-class Jewish family in Budapest in 1905, he saw the security of bourgeois life swept away by war and revolution. In response to extreme nationalism and anti-Semitism he was drawn to a succession of Utopian ideologies: first Zionism, then Communism. Both promised to normalise the Jewish condition: one by giving the Jews their own country, the other by dissolving ethnic and national identities altogether.
In this sense, Koestler's experience was specific. It was so particular that he played down his Jewishness for fear it would limit his appeal as a writer and political activist. He could not foresee that ethnicity and identity would be universal themes from the late 1960s. His ambivalence towards his origins, his experience of coming from a despised and displaced minority, represents the daily tragedy of people from East Timor to Kosovo.
Zionism proved too parochial for a cosmopolitan Jew like Koestler: assimilation and its corollary, self-hate, had corroded his cultural roots too much to replant them successfully in Israeli soil. Communism also failed him. Although the Soviet Union officially banished anti-Semitism, it was equally repressive of Jewish particularity. The promise of universal salvation became the justification for tyranny and suffering.
Koestler was one of the few intellectuals to challenge Communist doctrine and Soviet power while the Soviet Union was at the height of its popularity. When reading Darkness at Noon (1940) today, it is necessary to recall the attacks it drew from the left. Koestler was the Rushdie of the Cold War. It is easy now to forget the sacrifices made by dissenters when the European intelligentsia was overwhelmingly anti-American, if not pro-Soviet.
From the mid-1950s Koestler wrote about science and attempted to forge a new political philosophy grounded in irrefutable scientific truths. While intellectuals and the public were polarised between the two cultures - science versus the humanities - his success in finding a mass audience was unusual.
Koestler grew up in a society which believed that science and reason would promote the betterment of mankind. By the 1920s, quantum physics and psychoanalysis had shattered the rationalistic understanding of the natural world and human nature. Koestler thus anticipated the estrangement from science that has typified recent decades. In mastering new discoveries and purveying them to a wide audience he blazed the way for the likes of Steven Pinker.
However, his private life was chaotic and he could treat women brutally. This poses the question of how much we can forgive for the sake of genius. In his day, women's voices were muffled and there was a genie morale - a morality that excused geniuses from judgement. Ironically, we are now more inclined to excuse a wife-batterer on account of his disturbed childhood than his brilliance. In Koestler's case there may be a connection.
Modernism, with its penchant for fragmented narratives, multiple perspectives and language games was pioneered by exiles and migrants. The avatars of post- modernism are likewise the location-less thinkers surfing the wave of globalisation.
Koestler's life exemplifies the complex relationship between ethnicity, psychology and creativity which informs culture today. It suggests that a compromised identity may generate violent tension as well as innovation. Koestler's achievements may rank among the glories of cosmopolitanism, but his misdemeanours cast a shadow over the cult of the rootless.
David Cesarani is the author of `Arthur Koestler: the homeless mind' (William Heinemann, pounds 25)