Spanish queen (1451-1504). She married Ferdinand of Aragon in 1469, leading to the unification of Spain's two largest kingdoms, Castile and Aragon, in 1479. During their reign, new roads were built, Spanish coinage was made standard, and the power of the aristocracy was reduced. Spanish law was also codified, and Ferdinand and Isabella themselves took over the administration of justice. They also made war on the Moors, who held part of southern Spain, capturing the Moorish stronghold of Granada in 1492.
Speaking of 1492, Isabella is probably best known in America as one of the few people who saw merit in Christopher Columbus' plan to sail west from Spain to establish a route to the Indies, leading, of course, to Columbus' journey across the Atlantic Ocean to the Americas.
On top of all that, they were behind the Alhambra Decree, which ordered all Jews out of the country, started the Spanish Inquisition, and established Spain as a major power in the world, creating the Spanish empire. On the bright side, she was firmly opposed to enslaving American natives and ordered Columbus arrested after he defied her and enslaved 1,200 natives.