Aragorn becomes King of Gondor after the War of the Ring is won. He is crowned King Elessar after the One Ring is destroyed and Sauron’s power collapses.
Aragorn’s claim comes from his descent from Isildur, the former king who established Gondor’s royal line. For much of the story, Aragorn travels as the Ranger Strider, hiding both his identity and his right to the throne. He later leads the forces of Gondor and its allies against Mordor, helping distract Sauron while Frodo and Sam reach Mount Doom.
A common mix-up is Lord Denethor, who is Gondor’s Steward rather than its king. Denethor dies during the war, while his surviving son Faramir remains an important leader. Éomer is also crowned—but as King of Rohan, not Gondor. Aragorn ultimately becomes the thirty-fifth King of Gondor and also restores the northern kingdom of Arnor, ruling both as the first king of the Reunited Kingdom.
After his coronation, Aragorn marries Arwen and rules for many years. In the film, Gandalf places the crown on Aragorn’s head; in Tolkien’s wider story, his royal title is King Elessar of the House of Telcontar.