Commander Costello commands the Spanish border guards, bearing a striking physical resemblance to Fidel Castro. His operational jurisdiction sees him relentlessly pursue the main characters across the Pyrenees mountains, frequently coordinating with Spanish police Inspector Garcia and Officer Martin. Costello appears in episodes including "The Railway of Destiny," "The Escape," "The Pursuit," "Goodbye Belle," and "The End of the Hunt," conducting border security operations focused on Belle.