He murdered his first wife Alice Corrigan and his lover, actress Arlena Marshall. He found Arlena's dead body at 11:45, but it was actually his wife posing as a corpse. Arlena was strangled after her body was discovered, an unique twist in the bibliography of Agatha Christie.
Agatha Christie's Poirot
In the Agatha Christie's Poirot episode adapted from the novel, he was portrayed by Michael Higgs.
Les Petits Meurtres d'Agatha Christie
In Ding Dingue Dong, the France Télévisions adaptarion of Evil Under the Sun, the parallel character of Patrick Redfern is Nathan Steiner. Here he murdered Arlena (named Clarisse Rodier), but there is no mention of a previous murder.