Gustaf Gründgens (December 22, 1899 - October 7, 1963) was one of Germany's most famous actors of the 20th century. His single most famous role was that of Mephistopheles in Goethe's Faust, which is by many still considered having been the best interpretation of the role ever given.

Gründgens was also involved in one of the most famous literary cases of 20th century Germany, as the subject of a book by Klaus Mann, son of Thomas Mann, who wrote a novel entitled "Mephisto", which was a barely veiled bellicose account of the life of Gründgens. The book portrayed its main character as having shady connections with the Nazi regime. A lawsuit ensued as well as a controversy about libel and the freedom of fiction. Anyhow, their relation was a complicated one, since Gründgens was at one point married to Erika Mann, Klaus' sister, and the three had together worked in the theater, and both men have been homosexuals, a topic avoided in the novel.