Who is Alexander, Czar of all the Russias (AKA M. le Comte du Nord) from Commodore Hornblower and what is their importance?

Alexander, the Czar of all the Russias, is described as a tall, pale, young man. He holds his title in heredity though his father was assassinated. Alexander is proper and collected as a national leader and carefully weighs his involvement with Napoleon. For years he has maintained problematic neutrality, which has angered Napoleon and therefore cannot be maintained indefinitely. Hornblower meets Alexander at a critical juncture and convinces the monarch that England is ready, willing, and capable of intervening in any conflict between Russia and France. Later, Alexander boards Nonsuch to determine whether Hornblower's assertions are true only for the commodore or for the entire English fleet. Aboard Bush's taut ship, Alexander realizes that the English navy can indeed deliver on Hornblower's promise. Shortly thereafter, open hostilities between England and France are enjoined. The Czar thereafter disappears from the narrative.