Alexander Korvo was a human who lived on Earth.
In 1911, Sherlock Holmes prevented Korvo from acquiring History of Earth Volume 36,379 by Kronos Vad, (AUDIO: The Adventure of the Bloomsbury Bomber) a book which contained information about a Gomagog invasion of Earth. (AUDIO: Kronos Vad's History of Earth (Vol. 36,379))
Dorian Gray later met him at one of Evan Morgan's parties, where he conducted a seance through which he released the Gomagog which the possessed Pamela St John-Edwards, but was defeated by Gray. Both Holmes and Gray attended Korvo's funeral in 1927. (AUDIO: The Feast of Magog)