Pratt began appearing in theatrical performances in Canada, and during this period he chose Boris Karloff as his stage name. Some have speculated that he took the stage name from a mad scientist character in the novel "The Drums of Jeopardy" called "Boris Karlov". However, the novel was not published until 1920, at least eight years after Karloff had been using the name on stage and in silent films, opening the possibility that the Karlov character might have been named after Karloff after the novel's author noticed it in a cast listing and liked the sound of it rather than simply being a coincidence. Warner Oland played "Boris Karlov" in a film version in 1931. Another possible influence was thought to be a character in the Edgar Rice Burroughs fantasy novel "H. R. H. The Rider" which features a "Prince Boris of Karlova", but as the novel was not published until 1915, the influence may be backward, that Burroughs saw Karloff in a play and adapted the name for the character. Karloff always claimed he chose the first name "Boris" because it sounded foreign and exotic, and that "Karloff" was a family name (from Karlov—in Cyrillic, Карлов—a name found in several Slavic countries, including Russia, Ukraine and Bulgaria).