(Freud is revered as the father of modern psychology. He was a committed atheist, and apparently an incestuous adulterer) Evidence has emerged that suggests Freud had an affair with Minna Bernays, his sister-in-law, who shared his apartment at Vienna's Berggasse 19, where Freud lived with his wife Martha and their six children.
A hotel ledger discovered by Franz Maciejewski, a German sociologist and specialist in psychoanalysis, shows that on August 13, 1898, Freud checked into a Swiss hotel...But when Freud checked into the Schweizerhaus (Swiss House) in Maloja, he signed the register "Dr Sigm Freud u frau", meaning "Dr Sigmund Freud and wife". Minna and Freud spent that night together in Room 11.
"Freud's first slip?" The Age. <http://www.theage.com.au/news/books/freuds-first-slip/2007/03/01/1172338791947.html> (25 April, 2007)