Infanta Isabella of Spain

Infanta Isabella of Spain (12 August 1566 – 1 December 1633) was, together with her husband Albert of Austria joint sovereign of the Hapsburg Netherlands in the Low Countries and the north of modern France. She was the daughter of Philip II of Spain.

Infanta Isabella in Ruled Britannia
Queen Isabella I ascended to the throne of England when the Spanish Armada conquered the realm in 1588. She had ancestors from the English House of Lancaster, which gave her a claim on the throne. She married the Austrian Prince Albert, her cousin and fellow Hapsburg, who became King of England through her. Though England was never integrated into the Spanish Crown on paper, Isabella and Albert were completely subservient to her father's ruling from Spain.

She restored Catholicism as the kingdom's official state religion, and oversaw the establishment of an English Inquisition and the introduction of Pope Gregory XIII's calendar as tools to enforce Catholic orthodoxy among the English. Her predecessor, Queen Elizabeth, had made Protestantism the official state religion, restoring that status to it after her own predecessor, Queen Mary Tudor had elevated Catholicism following Henry VIII's favoritism of the Protestant sect which he had created over Catholicism. Throughout her monarchy, she was supported by a large Spanish army but was also supported by a sizable English garrison, as well as Irish troops. Isabella also minted silver and copper coins bearing her and her husband's double portrait, though they never displaced completely the old coins bearing Elizabeth I's image that still remained in circulation. Isabella's complexion, dark even for a Spaniard, caused many English people to remark on her resemblance to a Moor. Isabella was overthrown in 1598 when the English, under the leadership of Robert Cecil, revolted against her government and restored Elizabeth to the throne. She and Albert narrowly escaped England with their lives.

Isabella was named for Queen Isabella of Castile, who had helped unify Spain a century before (and had supported Christopher Columbus' exploratory journey to the New World). During her reign over England, Isabella was in the audience when a play honoring her namesake and written by Spanish soldier and playwright Lope de Vega debuted.

Literary comment
In OTL, Isabella did not marry Albert until late 1598 or early 1599, after Philip II's death, while in Ruled Britannia he has been her husband for a while before 1597. While this discrepancy is not addressed in the novel, it is explained by Harry Turtledove in the novel's afterword: Philip II had intended to marry his daughter to an Austrian prince long before that date, and Albert was the most obvious candidate. With Isabella needing to solidify her position as Queen of England, she would likely marry earlier and try to have children as soon as possible. The couple does not seem to have been more lucky in RB than in OTL, where all their children were miscarried or died in infancy.