In one interpretation, Kinbote is in fact a failed Eastern European academic probably named Vseslav Botkin, teaching at the same university as Shade.
The concept of a land called Zembla originates in Epistle II of Alexander Pope's An Essay On Man, which includes the cryptic lines: Ask where's the North!
Brian Boyd's book Pale Fire: The Magic of Artistic Discovery thoroughly explores the authorship and interpretive options, eventually settling on a thesis involving intervention in the text by both Shade and his daughter Hazel after their respective deaths.
Mary McCarthy, in her 1962 New Republic essay "A Bolt from the Blue" (in which she classed Pale Fire "one of the great works of art of the century"), identified the book's author as Professor V.
[1] Nabokov himself endorsed this reading, including in a list of possible interview answers at the end of his 1962 diary, "I wonder if any reader will notice the following details: 1) that the nasty commentator is not an ex-king and not even Dr. Kinbote, but Prof. Vseslav Botkin, a Russian and a madman ..." [2]