Brego was a horse of Rohan, who appears in Peter Jackson's film adaptations of The Lord of the Rings: The Two Towers and The Lord of the Rings: The Return of the King. He does not appear in any of the books, though he appears to take his name from the former king of Rohan named in the books.
After his rider's death, Brego became wild and refused to accept any new rider, until Aragorn met him in the stables of Edoras. Aragorn later then decided to turn him free, saying that he "has seen enough of war."
On the way from Edoras to Helm's Deep, after Aragorn was unhorsed and presumed killed in a battle with Warg riders, Brego found him floating in a river and nudged him awake, carrying him to Helm's Deep in time to bring warning of Saruman's approaching army of Uruk-hai.
Aragorn also rode Brego to the entrance to the Paths of the Dead, though he refused to go any further. The two of them were later reunited in Minas Tirith and Aragorn rode Brego to the Morannon to confront Sauron's forces. It is not known whether Brego survived the battle, since Aragorn fought on foot.
According to the cast commentary on the extended version of The Two Towers, Brego was played by a horse named Uraeus; Viggo Mortensen liked the horse so much that he purchased him after production wrapped.