Charles Angelo Siringo, cowboy, author, and detective, was born on February 7, 1855, in Matagorda County, Texas. His father, Italian immigrant Antonio Siringo, died a year later, leaving the boy's Irish mother, Bridgit (White) Siringo, to care for him and his older sister. After some schooling he made several trips on the Mississippi from New Orleans to St. Louis and back. In 1870 Siringo was in Texas, where he secured work as a cowboy. For six years he worked in the Texas coastal plain region for Joseph Yeamans, W. B. Grimes, and others. For nearly two years in 1871–72 he was employed as a cowboy by Jonathan E. and Abel H. (Shanghai) Pierce on their Rancho Grande near present-day Blessing. In 1876 Siringo became a trail driver and accompanied a herd of 2,500 longhorns over the Chisholm Trail from Austin to Kansas. He made a second trip in 1877 with one of the George W. Littlefield herds, following the trail's western branch. In Dodge City he signed on with David T. Beals and W. H. "Deacon" Bates to drive a herd into the Panhandle to establish the LX Ranch. During his years as an LX cowboy Siringo met the young outlaw Billy the Kid (see MCCARTY, HENRY). Later he led a posse of cowboys into New Mexico in pursuit of the Kid and his gang. In 1884 Siringo married Mamie Lloyd and soon thereafter left the LX to become a merchant in Caldwell, Kansas. It was then he began writing his first book. Published in 1885, A Texas Cowboy; or, Fifteen Years on the Hurricane Deck of a Spanish Pony established Siringo's fame as the first cowboy autobiographer, and went on to become a range literature classic. In 1886 Siringo moved to Chicago, where he obtained employment with Pinkerton's National Detective Agency. For the next twenty-two years he worked all over the West as an exceptionally shrewd and successful cowboy detective, even tracking outlaws as far north as Alaska and as far south as Mexico City. Throughout his detective career Siringo was also frequently involved with conflicts with early labor unions. He participated in such celebrated cases as the Haymarket anarchist trial, the Coeur d'Alene miners strikes, and the trial of Western Federation of Miners Secretary "Big Bill" Haywood, who had been charged with the dynamite murder of former Idaho governor Frank Steunenburg. Although he was reputed to be a fine shot, Siringo was proud of the fact that he made most of his arrests without violence.

In 1890 Siringo's wife died, leaving him a widower with a five-year-old daughter. Three years later Siringo met and married Lillie Thomas of Denver. The marriage ended in divorce after a son was born in 1896. He may have contracted one and possibly two other unsuccessful marriages. After leaving the Pinkerton Agency in 1907 Siringo retired to his ranch in Santa Fe, New Mexico, where he wrote his second book; this one detailed his experiences as a Pinkerton detective. The original title was "Pinkerton's Cowboy Detective," but a lawsuit by the agency held up publication for nearly two years and forced Siringo to delete the name "Pinkerton" from the title and throughout the book. It was finally published as simply A Cowboy Detective (1912) with fictitious names replacing real ones. To vent his anger against the Pinkertons, Siringo wrote and clandestinely published a third book, entitled Two Evil Isms, Pinkertonism and Anarchism (1915). The Pinkertons not only succeeded in suppressing the book, they sought the extradition of Siringo from Santa Fe to Chicago to face charges of criminal libel. New Mexico governor William C. McDonald, a personal friend of Siringo's, refused the extradition request, and the matter was dropped. In 1916 Siringo was appointed a New Mexico Ranger and for two years saw active service against cattle rustlers in the southeastern part of the state.

Following his return to Santa Fe Siringo published A Lone Star Cowboy (1919), which he said was to take the place of A Texas Cowboy, on which the copyright had expired. This was followed by History of "Billy the Kid" (1920). Failing health and financial insolvency forced him to abandon his ranch and leave Santa Fe in 1922. He moved to Los Angeles, California, since his children lived nearby. In poor health and living on the threshold of poverty, Siringo tried to support himself through the sale of his books. He even flirted with the idea of becoming a cowboy actor in western movies or a screenplay writer. He worked as a film advisor and played bit parts as an extra, probably due to his friendship with silent screen star William S. Hart. In 1927 Houghton Mifflin Company published Riata and Spurs, a mature composite of his first two autobiographies and his only book issued by a major publisher. But Siringo's old nemesis, the Pinkertons, stopped publication by threatening a lawsuit. The book was reissued later that year with a revised subtitle and substituted material on outlaws replacing Siringo's detective experiences.

Siringo liked to write about four themes: his youth and life as a cowboy; Billy the Kid, whom he had known personally and pursued; his twenty-two years as a Pinkerton detective; and outlaws with whom he had come in contact or knew about. Due in large part to his books, Siringo's prowess as a cowboy and Pinkerton detective made him widely known in his lifetime; he met United States Senators, state governors, and national officials, such diverse celebrities as Patrick (Pat) Garrett, Bartholomew (Bat) Masterson, Clarence Darrow, Charles M. Russell, Eugene Manlove Rhodes, William S. Hart, and Will Rogers, and a panoply of Western badmen. Siringo's experiences as the quintessential cowboy and determined detective helped romanticize the West and its myth of the American cowboy. He died in Altadena, California, on October 18, 1928.