Policeman

He made it impossible to be nobody. Before him, the British police had no reliable way to prove that the man in front of them was the man who had done it — names were given freely and falsely, faces were argued over in court, and a criminal with a fresh name in a new district was effectively a new person. Then, in 1905, an elderly shopkeeper and his wife were beaten to death in Deptford, south London, and a single greasy thumbprint was lifted from the emptied cash box. It matched a man named Alfred Stratton. He and his brother were hanged. It was the first murder conviction in British history secured by a fingerprint, and it happened because Edward Henry had spent fifteen years building the filing system that made the match findable.

That is the part people miss: the discovery was not that fingerprints are unique — Francis Galton had already established that. The problem was retrieval. A hundred thousand prints in a drawer are worthless if it takes a month to search them. Henry devised a classification that reduced any set of ten fingers to a code, sorting every record into one of over a thousand pigeonholes, so a clerk could go from a card in hand to a name in minutes. He brought it to Scotland Yard in 1901 and stood up the Fingerprint Branch. Within a few years it was the standard across the Empire, and then most of the world. As Commissioner of the Metropolitan Police he ran London through the Houndsditch murders and the siege in Sidney Street, when armed Latvian revolutionaries shot dead three unarmed constables in the City and the survivors were burned out of a house in the East End with the Home Secretary standing in the street watching.

He worked it out in India, on a problem that had nothing to do with murder. He was born in Shadwell, in the East End, the son of a doctor, and went out to the Indian Civil Service as a young man, ending up Inspector-General of Police in Bengal — responsible for policing a population larger than Britain's with a force that could not read most of the names it wrote down. Identity was the whole difficulty: land claims, pensions, contracts, repeat offenders, all resting on whether a man was who he said he was. Two Indian officers under him, Azizul Haque and Hem Chandra Bose, did the mathematics that made the classification work. Henry's name went on it. Theirs did not, until much later.

In 1912 a man shot him three times outside his own home in Kensington over a refused taxi licence. He survived, and he asked that the sentence be reduced. He resigned in 1918 after the London police went on strike over their own pay, which he had not fixed, and he died at Ascot in 1931 in retirement. The system he built is still in every police force on earth.

Forget the classification and the thousand pigeonholes. Remember only this: he spent his life making certain that any man in London could be told, definitively and against his own account of himself, exactly what he was.