Adolf Hitler lived with a Jewish landlord for almost 10 years while he plotted his rise to power and the eventual genocide of six million Jews.

Hitler took a small room in the Munich house of Jewish merchant Hugo Erlanger throughout most of the 1920s despite being imprisoned for a failed coup and publishing Mein Kampf in the first half of the decade.

According to a German historian, Hitler treated Erlanger with cordiality and respect — even during visits from senior Nazis at the apartment on Thierschstrasse 41 in the Lehel district.

"I must admit that I found Hitler quite sympathetic," Erlanger said of Hitler, who lodged with him between 1920 and 1929.

He added: "I often met him on the stairs or at the entrance — usually he was just writing something into a notebook — and usually he exchanged quite a few non-committal words with me.

He never gave me the feeling that he looked at me differently from other people," Erlanger told a Hitler biographer in 1934, according to historian Paul Hoser, as reported in The Times.

He married a non-Jew and kept a low profile while his tenant orchestrated a political project that would bring about the Holocaust.

"Since I am a Jew, I took as little notice as possible of the activities of my resident and the National Socialists," he said.

It is unlikely that Erlanger's remained so measured in his appraisal after he was arrested in 1938 and sent to a labour camp but survived the war.

In September 1930, shortly after Hitler moved from the address, the Nazi Party made huge gains in the German federal election, increasing their number of seats from 12 to 107.

Erlanger regained ownership of the building in 1949 after the end of WWII.