The sword Bilbo Baggins finds in the trolls’ hoard in The Hobbit is Sting. Bilbo discovers it alongside two larger Elvish blades, Glamdring and Orcrist.
Because Sting is short enough for a human-sized warrior to use like a dagger, Bilbo carries it as a sword. Its most distinctive magical property is that its blade glows blue when Orcs or other nearby enemies are present.
Bilbo later uses Sting during his adventures, including his encounter with giant spiders in Mirkwood. He gives it the name Sting after that fight. The weapon is eventually passed to Frodo Baggins, who carries it during the quest to destroy the One Ring. Glamdring belongs to Gandalf, while Orcrist is associated with Thorin Oakenshield.