This contribution aims to trace the thread of critical investigation developed by Luigi Lucchini in a long essay, largely forgotten by most but widely cited in the field of legal history, titled I semplicisti (antropologi, psicologi e sociologi) del diritto penale (1886). This work still stands as a formidable critique of criminological positivism, that is, of those whom Lucchini labels as “simplists,” who appear to be the forerunners of today’s penal populists. Their actions, depending on the case, could be said—more or less explicitly—to embody what is here proposed as the fundamental populist trait: “simplism.” The following analysis, therefore, seeks to highlight the continuities and differences between past and present penal populism, starting with a brief historical contextualization of Lucchini’s work.