Ken Livingstone never looked like a politician built for Britain’s establishment. He spoke plainly and didn’t bother to hide what he thought. While others in Labour trimmed and triangulated, he turned London into a stage for class conflict. From County Hall, just across the Thames from Parliament, he needled Margaret Thatcher and gave the capital’s working-class and marginalized communities a new sense of swagger and defiance. For some, he was a populist menace; for others, the only voice of sanity in an age of reaction. Either way, “Red Ken” showed that socialism in the UK could still make noise — and even win.

The conservative journalist Charles Moore once described Livingstone as “the only truly successful left-wing British politician of modern times.” It’s hard to disagree. Loathed and loved in equal measure, he was arguably Britain’s first modern celebrity politician, anticipating the more populist and reactionary figures that have since come to dominate UK politics. Yet more than just a memorable persona, Livingstone’s two stints running London, as leader of the Greater London Council (GLC) from 1981 to 1986 and as mayor from 2000 to 2008, transformed Britain’s capital and revealed the inspiring possibilities — and sobering limitations — of what a radical social democratic authority could achieve in a single city.