Richard Mardukas is an overly protective aide of Tessa's who insists on guarding her with his life. He holds the rank of Commander and is in charge of Mithril's TDD-1 when the Captain, Testarossa, is not on board; appropriate, given that Mardukas' position is that of Executive Officer. Mardukas is often seen wearing a hat bearing the name of the HMS Turbulent (S87), a real British submarine.

(Source: Wikipedia)