Mr. Thornsby is the security guard at the Coolsonian Museum.
He is a big, tall, and well-built African American male with a black mustache.
He is suspicious of visitors, and very adamant about finding any theives who'd be stealing from the the museum, and taking them down.
A Pup Named Scooby-Doo
He suspected Shaggy Rogers and Scooby-Doo of stealing the swords after they were taken because they were in the room at the time. His boss, Mr. Dayton, threatened to fire him if the swords weren't found by the time he left for his vacation. He was a suspect of being the Samurai Ghost, but was found innocent and took Mr. Dayton to the police station after Dayton was unmasked.