Stage name of construction engineer turned opera baritone Leonard Borland, in the short comic novel Career in C Major by James M. Cain. First published in 1943.
Cain wrote the story, originally titled Two Can Sing in 1937, and sold it to 20th Century-Fox, who turned it into the 1939 film Wife, Husband and Friend, with Logan/Leonard played by Warner Baxter.
Then the novel was published in the collection Three of a Kind in 1943, and titled Career in C Major.
Then it was adapted to film again in 1949 as Everybody Does It, with the role played by Paul Douglas.