Robert Olmstead is the narrator of The Shadow Over Innsmouth and a member of the Marsh family. His home is in Toledo. It is remarked that his eyes have the same, strange quality seen in descendants of Obed Marsh. In the story's final pages he learns he is the great-great-grandson of Obed Marsh and a Deep One and in time will become one of the amphibious monsters he witnessed in Innsmouth.
His name is never given within the story, but Lovecraft did give it in one of his letters.