This paper aims to honor the memory of the alienist Louis Delasiauve (1804–1893). His classification of the different types of epilepsy based on clinical symptoms is still relevant today and made him a precursor of contemporary epileptology. In 1851, Delasiauve clinically and etiologically isolated ‘acute mental confusion’ (acute confusional state) from all other forms of dementia. Never deviating from his republican and progressive ideals, he devoted himself throughout the 19th century to treating those insane asylum patients who received the poorest care: epileptics and children with intellectual disabilities. Studying functional cognitive disability as well as mental disability secondary to congenital malformations, Delasiauve developed a novel specific form of pedagogy to deal with delays in cognitive development. This made him one of the initiators of institutional pediatric psychiatry. His ideas would be carried forward by his favorite student, Désiré-Magloire Bourneville (1840–1909). Committed to social welfare, Delasiauve worked relentlessly to improve access to healthcare for the least fortunate throughout France. As a passionate supporter of universal, free and secular education, he participated in a major movement away from religious establishments that involved opening a public school in every French canton.