Arthur Morgan was born circa 1863 to Beatrice and Lyle Morgan in the northern US. As a child, his mother died of unknown causes, while his father was a petty criminal and outlaw. In 1874, when Arthur was 11 years old, his father was arrested for larceny. Morgan later witnessed his death and, despite a strained relationship with him, still donned his hat and kept a picture of him.

Around 1877, Arthur was found as a 'wild delinquent' and picked up off the streets by Dutch van der Linde and Hosea Matthews.[4] Viewing the pair as surrogate father figures, Arthur came to share Dutch's vision of a life lived free from the constraints of civilization and the rule of law. The pair taught him how to read, write, hunt, fight, shoot, and ride, becoming their first protégé as well as one of the founding members of the Van der Linde gang.