A French schoolmaster whom Archer meets in London. Archer finds him intellectually engaging, but May thinks him too socially inferior for them to associate with. He’s considering moving to New York for the intellectual life which he doesn’t realize is nonexistent there. Later, Archer discovers that M. Rivière is also the secretary who helped Ellen escape her husband, and with whom she is rumored to have had an affair. Though Count Olenski sends M. Rivière to convince Ellen to return to him, M. Rivière begs Archer not to let Ellen do so, as he believes the Count to be a brute.