Cardinal Richelieu acts as prime minister to King Louis XIII and serves as the series' primary political antagonist. He masterminds intricate court schemes to consolidate his power, including a plot to disgrace Queen Anne of Austria by manipulating her association with the Duke of Buckingham. This maneuver aims to weaken her standing and further his own ambitions.

His appearance abandons traditional cardinal red, consistently featuring all-black garments instead. This visual choice streamlines his clerical status for the adaptation.

Richelieu relies on a network of agents to advance his plans. Spies Milady de Winter and Captain Rochefort act as his key operatives. Milady conducts espionage and sabotage, deploying her trained parrot to surveil the queen, while Rochefort commands the Cardinal's Guards and clashes directly with the musketeers. These agents embody Richelieu's authority across the narrative.

Despite his antagonistic tactics, Richelieu demonstrates unwavering loyalty to King Louis XIII. He consistently works to influence royal decisions rather than pursue outright overthrow, adhering to his perceived duty to the monarchy. This loyalty proves flexible during the Iron Mask crisis, where he temporarily allies with the musketeers to protect the true king from a usurper. His cooperation involves aiding prison escapes and coordinating resistance against the impostor ruler.

Richelieu exhibits pragmatic adaptability when confronting existential threats to the French crown. Imprisoned by the false king's regime, he assists Athos and Rochefort in breaking free. Later, he forges a combined force of musketeers and Cardinal Guards to storm Iron Mask's fortress, placing national stability above personal rivalries.