In the second half of the 19th-century, a group of psychiatric experts discussed the relation between brain malfunction and moral misconduct. In the ensuing debates, scientific discourses on immorality merged with those on insanity and the brain. This yielded a specific definition of what it means to be immoral: immoral and insane due to a disordered brain. In this context, diverse neurobiological explanations for immoral mind and behavior existed at the time. This article elucidates these different brain-based explanations via five historical cases of immoral persons. In addition, the article analyses the associated controversies in the context of the period's psychiatric thinking. The rendering of the immoral person as brain-disordered is scrutinized in terms of changes in moral agency. Furthermore, a present immoral person is discussed to highlight commonalities and differences in past and present reasoning.