The subject of this article originates from non-canonical sources. To find out about what is considered "canon" see LOTR:Canon.
He is non-canonical as he never appears in the books.
During the War of the Ring, Halladol was among hundreds of Elves that accompanied Haldir of Lorien to the fortress of Helm's Deep on March 3, 3019. There, he and the elves aided the people of Rohan and their king, Theoden, in defending Helm's Deep from Saruman's army of 10,000 Uruk-hai that were marching towards the fortress. Celebrílad was stationed on the Deeping Wall, and demonstrated his unmatched proficiency of archery, as he and the elves loosened devastating hails of arrows in seconds, killing many Uruk-hai that were charging towards the Hornburg and the Deeping Wall. Halladol was among the elves that died defending the keep during the Battle of Helm's Deep.