The Mercenary (Italian: Il mercenario), known in the UK as A Professional Gun, is a 1968 Zapata Western film directed by Sergio Corbucci.

The film stars: Franco Nero, Jack Palance, Tony Musante, Eduardo Fajardo and Giovanna Ralli, and features a musical score by Ennio Morricone, taking inspiration from his work in Guns for San Sebastian, and Bruno Nicolai.

On the northern side of the Mexico–United States border, Sergei "Polack" Kowalski, a well-groomed, greedy mercenary, attends a circus performance where he recognizes the show's lead rodeo clown as Paco Roman.

Colonel Garcia's troops arrive to attack them, and Kowalski agrees to help Paco fight them for money.

However, Columba executes her plan, and holds Garcia at gunpoint while the circus performers create a diversion.

Using two machine guns, Paco and Kowalski kill most of Garcia's troops, and they escape with Columba and the performers.

The group splits up; Columba and the performers leave to spread the word of Paco's return to Mexico, Paco prepares to lie low before reuniting with Columba, and Kowalski, who has been given a share of his own reward money, prepares to leave Mexico.

As the two friends part ways, Colonel Garcia and four soldiers prepare to ambush and kill Paco.