Short answers, pulled from the story.
Elrond Half-elven is a fictional character in J. R. R. Tolkien's Middle-earth legendarium, born in the First Age to the half-elven mariner Eärendil and Elwing. He is master of Rivendell and bearer of Vilya, the Ring of Air, one of the three Elven Rings. He lived in Rivendell through the Second and Third Ages of Middle-earth before departing over the Sea at the approximate age of 6,520.
Vilya is called the Ring of Air and is one of the three Elven Rings. It was originally held by Gil-galad, the last High King of the Noldor, who entrusted it to Elrond along with another ring given to Círdan at the end of the Second Age. Tolkien wrote that after the destruction of the Ruling Ring, the Three Rings of the Eldar lost their virtue.
Elrond established the refuge of Imladris, later called Rivendell, after Sauron destroyed Eregion and surrounded his army during the War of the Elves and Sauron in the Second Age. Relief came when the dwarf-king Durin and the elf-king Amroth attacked Sauron's rear, allowing Elrond to retreat north into a secluded valley where he built the refuge.
Elrond would permit Arwen to marry Aragorn only if Aragorn became High King of both Gondor and Arnor. The Tolkien scholar Richard C. West describes this not as cruelty but as giving Aragorn the incentive to fulfill what was already his hereditary duty, while securing his daughter's future.
Tolkien almost never writes "Lord Elrond", preferring "Master Elrond". Christine Larsen, writing in the Journal of Tolkien Research, argues the usage was deliberate and reflects the meaning of mastery in Tolkien's world: skill and authority rather than ownership. Elrond is described as "the greatest of lore-masters", and lore-mastery was the defining characteristic of the Noldor Elves, whose name itself carried that meaning.
Cyril Ritchard voiced Elrond in the 1977 Rankin/Bass animated Hobbit, André Morell in Ralph Bakshi's 1978 Lord of the Rings, and Paul Frees in the 1980 Rankin/Bass Return of the King. Hugo Weaving portrayed the character across all six of Peter Jackson's Middle-earth films and reprised the role in two video games. Robert Aramayo plays a younger Elrond in the 2022 television series The Lord of the Rings: The Rings of Power.