After the War of the Ring, Aragorn takes the royal name Elessar. The name means “Elfstone” and becomes his formal title as king of the reunited kingdoms of Gondor and Arnor.
Elessar is connected to the green Elfstone associated with Aragorn and Arwen. In Tolkien’s history, Galadriel gives the stone to Aragorn, and it symbolizes healing, renewal, and his rightful return to kingship. Arwen’s name for him, Elessar, becomes especially important during his coronation.
Aragorn is crowned after Sauron’s defeat and becomes the first High King of the Reunited Kingdom. He is the twenty-sixth King of Arnor and the thirty-fifth King of Gondor. His royal house is called Telcontar, the Quenya form of “Strider,” another of his names.
Thorongil was an earlier alias Aragorn used while serving in Gondor and Rohan. Elendil and Isildur were earlier kings and ancestors in his line, so they are related to his royal history but are not the name he adopts as king.