It was the greatest intellectual partnership. Two personalities fizzing with talent, united in mutual affection and burning with passion for a shared cause. It is idle, the German socialist Wilhelm Liebknecht observed, to inquire after who contributed what to the joint enterprise, for Marx and Engels were "one soul - inseparable in all their working and planning". Underpinning the political and theoretical collaboration was a friendship of epic depth and durability. After Marx's death, in 1883, the former Chartist Julian Harney sent the grieving Engels a letter of condolence. "Your friendship and devotion, his affection and trust, made the fraternal connection of Karl Marx and Friedrich Engels something beyond anything I have known in other men. That there was between you a tie ‘passing the love of women' is but the truth."
Like many other male cultural partnerships - Goethe and Eckermann, Johnson and Boswell, Laurel and Hardy - the Marx-Engels consortium worked because one partner was willing to accept (perhaps avow would be a better word) the superiority of the other. "Marx was a genius; we others were at best talented," Engels declared after his friend's death. It never occurred to him to be resentful of Marx's eminence: "To be envious of something like that one must have to be frightfully small-minded." And Engels practised what he preached: for decades, he put his own intellectual development on hold while he worked to support Marx and his family. Without this system of self-effacement, a long-term friendship with Marx, the alpha beast in the jungle of 19th-century socialism, would quite simply have been unworkable.
Writing a biography of Engels thus poses a challenge: the subject has to be pulled out, as it were, from under Marx's legacy. He also has to be restored to his 19th-century context, for Engels was a German Romantic and a Victorian businessman and intellectual before he became the prophet of Soviet and Chinese communism. In this splendid, gripping biography, Tristram Hunt triumphantly masters both problems. His witty, humane and sharp-eyed portrait of Engels does justice to the complex chemistry of the relationship with Marx, but also sets the "junior partner" at the centre of his own life and intellectual evolution.