The event
The Reunited Kingdom is established under King Elessar as the dominion of Men begins.
On the dating
The counting of the Fourth Age begins at different points in different reckonings.
Consequences
The Elves wane and depart; Men inherit Middle-earth; the great tales pass into history and legend.
Participants
CharacterAragorn
The heir of Isildur, raised in Rivendell in secret, who becomes King Elessar and reunites the kingdoms of Gondor and Arnor.
CharacterArwen Undómiel
Daughter of Elrond who chose mortality to wed Aragorn, uniting the lines of Lúthien and Beren.
CharacterSamwise Gamgee
Frodo’s loyal gardener and companion, who carried him — and, briefly, the Ring — to the end of the quest.
Sources
The Lord of the Rings · 1954–55
Three volumes: The Fellowship of the Ring, The Two Towers, The Return of the King.