The Mucker is a novel by Edgar Rice Burroughs. Originally two stories, The Mucker begun in August 1913 and published by All-Story Weekly in October and November 1914; and The Return of the Mucker begun in January 1916 and published by All-Story Weekly in June and July 1916. The book version was first published by A. C. McClurg on 31 October 1921. From January 1922 to August 1939, Methuen (UK) published a version of The Return of the Mucker under the title The Man Without A Soul.

Billy Byrne is a low class American born in Chicago's ghetto. He grows up a thief and a mugger. "Billy was a mucker, a hoodlum, a gangster, a thug, a tough." He is not chivalrous nor kind, and has only meager ethics - never giving evidence against a friend or leaving someone behind. He chooses a life of robbery and violence, disrespecting those who work for a living. He has a deep hatred for wealthy society.

He trains as a prizefighter but cannot stop drinking. When falsely accused of murder, he flees to San Francisco and is shanghaied aboard a ship. Enforced sobriety, brutal ship's discipline and productive work improves him. The ship's secret mission is soon enacted - the hijacking of a specific yacht to take a millionaire's daughter, Barbara Harding, for ransom. Billy Byrne brutally beats her suitor, Billy Mallory, leaving him for dead.

"He knew that she looked down upon him as an inferior being. She was of the class that addressed those in his walk of life as 'my man.'" After Barbara confronts him and calls him a coward, a change begins in Billy Byrne. He saves the life of one kidnapper, Theriere, rather than letting him be washed overboard, though he cannot fathom his own reasons. After a terrible storm, the ship is damaged and only makes it to land with Billy's help at the wheel. He rescues Barbara from the wreck and brings her ashore. Barbara is kidnapped by headhunters descended from medieval Japanese. Byrne and Theriere race to rescue her from the daimyo's hut in the middle of the village, but Theriere is fatally wounded in the escape.