Who is Karl Heinrich von Altberg-Ehrenstein from Dagon and Other Macabre Tales and what is their importance?

Karl Heinrich von Altberg-Ehrenstein is a character in the story, The Temple. He was a Lieutenant Commander in the Imperial German Navy during World War I and commanded the submarine that successfuly sunk the British freighter Victory. After a failed mutiny attempt, Karl's submarine was severely damaged and sunk to the bottom of the ocean where he found an ancient city.