Aragorn becomes king of Gondor in J.R.R. Tolkien's The Lord of the Rings.
Gondor is one of the principal realms of Men in Middle-earth. It was founded by Elendil and his sons after the fall of Númenor, with Minas Anor and Minas Ithil as important early cities. Minas Anor later becomes Minas Tirith, the realm's capital and chief defensive stronghold.
By the time of the War of the Ring, Gondor is weakened by centuries of conflict and is ruled by stewards rather than kings. Aragorn is the heir of Isildur, so his claim restores the royal line that has been absent from Gondor for many generations.
Rohan is a neighboring kingdom famous for its horse-lords. Arnor is the northern realm founded by Elendil, while Moria is an underground Dwarven city rather than a kingdom ruled by Aragorn.