Mr. Thornsby is the security guard at the Coolsonian Museum.
Mr. Thornsby is a big, tall, and well-built African American male with a black mustache.
Thornsby is serious about handling security at the museum, and is suspicious of visitors, and very adamant about finding any thieves 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 possible suspect of being the Samurai Ghost, but was found innocent and thanked the gang for finding the swords and apologizing to Shaggy and Scooby for falsely accusing them. After they unmasked the Samurai Ghost as Mr. Dayton, Thornsby then proceeded on taking Dayton to the police station.