Marvin Lewis (1907 - October 5, 1991) was a city supervisor of San Francisco, California from 1944 to 1955. After his days as a supervisor, he went into private law practice, where he became famous for taking and winning frivolous lawsuits involving psychological damage. The most famous of these was a 1970 case in which he sued the City of San Francisco on behalf of a woman who claimed a cable car accident had turned her into a sex maniac.
In 1947, a politician named Marvin appeared alongside Diana McGraw at a Mothers Against the Madness in Germany event in San Francisco. After the event Marvin and a number of other Bay Area politicos hosted a dinner in McGraw's honor, and after the dinner Lewis offered to drive the tipsy McGraw back to her hotel on the other side of the city. At the hotel, Marvin asked McGraw if he could join her in her room for a nightcap. Against her better judgment, McGraw let him in and the two had a gratuitous one-night stand. McGraw would later feel very guilty about the affair but would also remember how pleasurable it had been.
Marvin meant so little to Diana that she never bothered to remember his last name.
Harry Turtledove does not specify that the character Marvin is indeed Marvin Lewis. However, Turtledove does provide sufficient biographical information about the character, which matches the historical figure.