Allan J. Pinkerton (25 August 1819 – 1 July 1884) was a Scottish American detective and spy, best known for creating the Pinkerton National Detective Agency. Born in Glasgow, Scotland, Pinkerton emigrated as a young man to seek his fortune in the United States of America. A self-educated man, he had little formal training in any of the professions usually available to immigrants. However, that never slowed the ambitious young man.

He settled in Dundee Township, Illinois, fifty miles northwest of Chicago. He built a cabin and started a cooperage (making barrels). His home soon became a stop on the Underground Railroad, smuggling escaping slaves northward to Canada.

Pinkerton worked with the local sheriff to identify some counterfeiters who were working nearby. Soon he was appointed as the first police detective in Chicago, Cook County, Illinois. In 1850 he partnered with Chicago attorney Edward Rucker in forming the North-Western Police Agency, one of the nation's first private detective services. The company later became Pinkerton & Co and finally Pinkerton National Detective Agency, still in existence today as Pinkerton Consulting and Investigations, a subsidiary of Securitas AB. 

Pinkerton's business insignia was a wide open eye with the caption, "We never sleep." People in the area soon started referring to the company as "private eyes," a term still in use today.

Pinkerton's agency solved a series of train robberies during the 1850s, and he soon had all the business the fledgling company could handle. He never seemed to be afraid of danger. In many cases he personally chased down and arrested dangerous criminals. As a staunch abolitionist, he attended the secret meetings held by abolitionists John Brown and Frederick Douglass in Chicago along with abolitionists John Jones and Henry O. Wagoner. At those meetings, Jones, Wagoner, and Pinkerton helped purchase clothes and supplies for Brown. Jones' wife, Mary, guessed that the supplies included the suit Brown was later hanged in after the failure of John Brown's raid on Harpers Ferry in November 1859.

During the first two years of the Civil War, Pinkerton served as head of the Union Intelligence Service and reportedly was involved in numerous dangerous undercover missions. He not only sent his men out as spies, but Pinkerton often personally became a spy himself. If captured, he undoubtedly would have been hanged.

After the Civil War, Pinkerton continued his pursuit of train robbers. He was hired to capture the infamous train robber Jesse James but failed at first. The railroad canceled the contract. Frustrated, Pinkerton refused to concede defeat. He continued to chase Jesse James at his own expense and even paid his employees out of his own pocket to continue the chase. He still failed and eventually gave up after James allegedly captured and killed one of Pinkerton's undercover agents (who was working undercover at the farm neighboring the James family's farmstead).

Allan J. Pinkerton continued to manage his detective agency and to find and apprehend outlaws, often doing the most dangerous work himself.

There is a bit of a question about the cause of Pinkerton's death. As an older man, he developed several ailments, including malaria, which he had contracted during a trip to the southern United States. He also suffered a mild stroke when he was about 65 years of age. However, the most common story is that this man – who had spent his life personally chasing many of the most dangerous outlaws in the country and being a spy in wartime – was walking his wife's poodle one day when the dog reportedly wrapped its leash around Pinkerton's legs. Pinkerton tripped, fell to the concrete, and severely bit his own tongue. He died of a gangrene infection of the tongue a few days later.

After Pinkerton spent a lifetime of danger, a poodle brought him down, something the most notorious badmen of the time had been unable to accomplish.

Allan J. Pinkerton is buried in Graceland Cemetery, Chicago.

References:

Wikipedia: https://en.wikipedia.org/wiki/Allan_Pinkerton

Encyclopædia Britannica: http://www.britannica.com/EBchecked/topic/461110/Allan-Pinkerton

Works by or about Allan Pinkerton at the Internet Archive: http://bit.ly/2v3Svjw