Ugluk is the leader of Saruman's Uruk-hai scouts in The Lord of the Rings books (and the movies after Lurtz is killed by Aragorn). He is an ill-tempered, vicious Uruk-hai leader who looks down on the Orcs accompanying him and his fellow Uruk-hai, and in fact outright kills Orcs who become insubordinate. The movie version takes it further by then cannibalizing the Orc he just beheaded along with his fellow Uruk-hai (also uttering the now famous line "Looks like meat's back on the menu, boys!").
Ugluk's fate in the books is ambiguous, but in the movies, when the Riders of Rohan led by Eomer attack him and his band, they kill all of the Uruk-hai (Eomer later confirms they left none alive). Though Ugluk's death is not shown on-screen, his severed head is later found mounted on a pike, proving that he was indeed killed.
He is playable in the Gameboy Advance version of the video game Lord of the Rings: The Third Age if the player is playing the evil campaign.