Duncan, also known as Man-At-Arms, is the leader of Eternia’s defenses, and is a loyal servant of Queen Marlena and King Randor. Man-At-Arms was the student of Rohad. He is a skilled and creative scientist, and is also very good at inventing. Being the innovator of technology and weapons for the royal family, Duncan is always making new devices and weapons for Prince Adam.
Duncan has a very strong friendship with Prince Adam, Orko, and Teela. Duncan is one of the only two adults, other than the Sorceress of Castle Grayskull, who knows about Prince Adam’s secret. After the death of her husband, the Sorceress of Castle Grayskull could not handle raising Teela and protect Castle Grayskull by herself, so Duncan adopted Teela. Duncan showed great care for Teela throughout the series.
Man-At-Arms is constantly pestered by Orko, who always messes with Duncan’s science equipment and shows Duncan magic tricks that often backfire on him. Orko is a Trollan magician and a Jester to King Randor, and also one of three people who know about Prince Adam’s secret.
In Battle, Man-At-Arms wields a Special mace that also can be changed into an inconspicuous baton. The Mace also has a computerized telescope able to see up to 25 miles with darkvision. Duncan also has a gun, which he calls his hand blaster, that can collapse into a thick bracelet. His hand blaster shoots out plasma, and can also launch small missiles.