Scottish-American detective (1819-1884). Born in The Gorbals, a very poor area in Glasgow, Scotland. Moved with his wife to Canada, then Illinois, where he worked as a cooper. After noticing a suspicious fire-pit on a remote island in 1846, Pinkerton and the local sheriff closed down a counterfeiting operation that was using the island as a hideout. After several other successful jobs in law enforcement, he became the first detective on the Chicago police force. In 1850, he founded the Pinkerton and Co. Detective Agency -- considered by many to be the first real private detective agency -- which became famous for its relentless pursuit of wrong-doers. One of his favorite tactics was undercover infiltration of criminal organizations. He introduced other techniques that have become very common in detection, including the use of mug books.
Pinkerton fervently believed that slavery should be abolished. He worked with the underground railroad and gave aid and shelter to Frederick Douglas and John Brown. He foiled an assassination attempt against Abraham Lincoln on the President's first trip to Washington after his election. He worked for a time as the spymaster for the Union during the American Civil War, but resigned before the end of the conflict (and later expressed regret, believing that he could have prevented Lincoln's assassination at Ford's Theater).
After recovering from a stroke, Pinkerton led the pursuit against the James Gang and helped destroy the Molly Maguires -- a controversial case, since many believe Pinkerton's activities were nothing more than union-busting.
After his death in 1884, the Pinkerton Agency became known primarily as an anti-labor goon squad -- despite Pinkerton's moderate pro-labor beliefs (though he opposed strikes and unions, so maybe he wasn't particularly pro-labor after all.)
Research from GURPS Who's Who 2, compiled by Phil Masters, "Allan Pinkerton" by James H. Hay, pp. 84-85.