Finally, the Colonel's unique physical state, never changing, and fresh as the moment he stepped out of the Fountain of Youth, means that he has no scar tissue and no damage to any of his organs or senses. His enhanced, werewolf body operates at peak efficiency, shrugging off any damage, even on the molecular level, in seconds. This grants the Colonel senses surpassing that of the average man, including excellent hearing, a keen sense of smell, and perfect vision.
Mostly though, having an Immortal main character holding the series together means never having to worry about the real passage of time, of the series becoming outdated, or the effects of aging limiting the efficiency of the protagonist. Like Dracula, Mark Kenslir is a timeless character who could be around for a very, very long time.