In Eliot's original poem, Old Deuteronomy is described as an ancient, wise cat who has "lived many lives in succession" and is respected by the other cats and humans in his environment. His name derives from Deuteronomy, the fifth book of the Old Testament of the Bible, which shares the central element of law with the character (who is a magistrate).
Cats expands on the theme of wisdom by depicting Deuteronomy as the leader of the show's Jellicle tribe, providing comfort and guidance to the other characters. Deuteronomy also has the task of making the "Jellicle Choice" and choosing the cat who can ascend to the Heaviside Layer (Also spelled "Heavyside"). Much of Cats' plot is fueled by this; several characters perform and try to convince Deuteronomy to choose them. At the end of the show, Deuteronomy is kidnapped by Macavity and restored by Mr. Mistoffelees. He then persuades the other cats to listen to the outcast Grizabella, selects her to be reborn, and escorts her to the Heaviside Layer.
Old Deuteronomy has three songs in Cats, including the final number, "The Ad-dressing of cats." He is traditionally played by strong lyric baritone performers. In the 1998 video version of the musical, Old Deuteronomy is portrayed by Ken Page, who also created the role on Broadway. In the original West End production, and accompanying album, he was played by Brian Blessed, who was also Bustopher Jones. Old Deuteronomy was also played by Jeff Leyton in the West End production of 'Cats'.