Francis Augustus Hamer (March 17, 1884 – July 10, 1955) was an American lawman and Texas Ranger who led the 1934 posse that tracked down and killed criminals Bonnie Parker and Clyde Barrow. Renowned for his toughness, marksmanship, and investigative skill, he acquired status in the Southwest as the archetypal Texas Ranger. He was inducted into the Texas Ranger Hall of Fame. His professional record and reputation are controversial, particularly with regard to his willingness to use extrajudicial killing even in an increasingly modernized society.

Hamer was commissioned as an officer of the Texas Highway Patrol, then seconded to the prison system as a special investigator charged with apprehending Barrow and his colleagues. Hamer balked at the compensation of $180 a month, less than half his current pay,but Simmons reiterated that Hamer would collect his fair share of the reward money. He further added to the deal by authorizing Hamer to take whatever he wanted from among the Barrow Gang's possessions when he caught them. Simmons said that he wouldn't presume to tell Hamer how to do his job, but he suggested that Hamer "put 'em on the spot, know you're right—and shoot everybody in sight."

Hamer examined the pattern of Barrow's movements, discovering that he essentially made a wide circle through the lower Midwest, skirting state borders wherever he could to take advantage of the fact that law officers could not pursue suspects across state lines. The circle's anchor points were Dallas, Joplin, Missouri, and northwest Louisiana, with wider arcs outward for bank robberies. Hamer felt that he learned Barrow's statistics, but "this was not enough. An officer must know the habits of the outlaw, how he thinks and how he will act in different situations. When I began to understand Clyde Barrow's mind, I felt that I was making progress."