Adolfe Durand was a French criminal mentioned in the foreword to the short story collection The Labours of Hercules. While reflecting on the mythological Hercules and his twelve labours, Poirot came to the conclusion that this Greek hero was nothing more than "a large muscular creature of low intelligence and criminal tendencies!" Poirot was reminded of Adolfe Durand, a French butcher who had been tried in 1895 in Lyon for the murder of several children. The defence during the trial was epilepsy. Whether this was "grand-mal" (tonic-clonic seizure) or "petit-mal" (absence seizure) had been much debated during the trial. To Poirot, Hercules certainly suffered from "grand-mal".
Adolfe Durand is most likely a fictional person as no references to an actual criminal by this name can be found.