Allan Pinkerton of the Pinkerton detective agency was born on this date in Scotland in 1819. Pinkerton emigrated to America as a young man, and his many accomplishments in this country include writing (or having written) a series of books about his detective agency with such titles as The Gypsies and the Detectives and Strikers, Communists, Tramps and Detectives.
As the first official detective in Chicago, Pinkerton used techniques that are still famous today, including "shadowing" a suspect and doing undercover surveillance. He is said to have thwarted an assassination attempt against Abraham Lincoln during the Civil War. (That's him (left) with Lincoln in a Wikipedia photo).
Pinkerton died in 1884, and at the time of his death he had been working on a way to keep track of all criminals in a central location--the same sort of database that the FBI uses today.