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The weathered-looking, middle-aged chief petty officer in the Royal Manticoran Navy has a habit of picking bar fights with Marines; the latter regard this as a compliment, making the correct assumption that he is looking for sufficiently tough opposition. Officially, he's a gunner's mate; unofficially, he's an expert smuggler and computer hacker. Although he cut back on his illegal activities after Commander Honor Harrington took command of the HMS Fearless, he continued to use his skills to choose his own assignments.
When the ship he was on was captured by the People's Republic of Haven (commonly called "The Peeps"), Horace feigned defection and joined the Havenite Navy. Since Havenite technology was far inferior to Manticore's, he was easily able to subvert the system and engineered a breakout, rescuing his captain from execution, as well as his crewmates and (ironically) a Havenite Citizen-Captain from indefinite banishment on a prison planet officially called Hades, but best known as Hell. For this, he received the Parliamentary Medal of Valor as well as a knighthood.
He is at least as tough as he looks but he also has a softer side: he mentored pilot Scotty Tremaine and young technician Aubrey Wanderman and eventually married Iris Babcock, a Marine. He remains attached to Scotty and has hacked the Bureau of Personnel database multiple times to remain in a post close to Scotty.