She has a French accent and is voiced by the late Eva Gabor (who voiced also Miss Bianca in The Rescuers), though Robie Lester provides her singing voice. In House of Mouse, she was voiced by the late Russi Taylor.
Duchess is a long-haired purebred white Turkish Angora cat with blue eyes later described as shining like sapphires. She wears a gold collar studded with what may be diamonds.
Duchess is very elegant, beautiful and ladylike, being the pet to an aristocrat. She is very devoted to her owner, Madame Adelaide Bonfamille.
She is kind and friendly to everyone. She is both caring and protective towards her children and also tries to encourage them to develop into proper members of French society.
She also is a connoisseur of music and presumably teaches her kittens to sing and play piano.
Duchess lives with her owner and retired opera singer, Madame Bonfamille, as well as her three kittens: Marie, Berlioz, and Toulouse in a large mansion on 1910 Paris.
At the beginning of the film, the family is returning from a carriage ride. Back home, Duchess oversees Toulouse's painting lesson and Marie and Berlioz's music lesson.
Later, Madame Bonfamille meets with her lawyer and dear friend, Georges Hautecourt.
After kissing Duchess's tail, (which the lawyer believes to be Madame Bonfamille's hand) they settle down to business.
Madame reveals that, after her death, she intends to leave her vast fortune to Duchess and her kittens.
At the end of their lifespan, Madame's butler, Edgar would inherit. Edgar overhears and plots to remove the cats from the inheritance as he believes he would die before getting to inherit.
That night, Duchess and the kittens are drugged using milk mixed with sleeping pills. Edgar catnaps Duchess and her kittens and leaves them in the French countryside.
The next morning, Duchess meets O'Malley, an alley cat, who offers to guide them back to Paris. They have a struggle returning to the city, briefly hitchhiking on the back of a milk cart before being chased off by the driver.
Marie subsequently falls into a river and is saved by O'Malley. Then, they meet a pair of English geese, Abigail and Amelia Gabble, who are travelling to Paris.
The group head off, marching like geese until they reach Paris and come across the girls' drunken Uncle Waldo. Abigail and Amelia then depart to take Waldo home.
Traveling across the rooftops of the city, the cats meet Scat Cat and his band, close friends to O'Malley who perform the song "Everybody Wants to Be a Cat".
After the band have departed and the kittens lie in bed, O'Malley and Duchess spend the evening on a nearby rooftop and talk while the kittens listen at a windowsill.
O'Malley offers to have Duchess stay and be with him, but she sadly turns him down, largely out of loyalty to Madame Adelaide.
The next morning, Duchess and the kittens make it back to the mansion, whereupon O'Malley departs sadly.
Edgar sees Duchess and kittens coming and captures them, placing them in a sack hidden in an oven. Duchess tells Roquefort to pursue O'Malley and get help. He does so, where O'Malley races back to the mansion, ordering Roquefort to find Scat Cat and his gang.
Edgar places the cats in a trunk which he plans to send to Timbuktu, Africa. O'Malley, Scat Cat and his gang of Alley cats and Frou Frou all fight Edgar, while Roquefort frees Duchess and the kittens.
In the end, Edgar is tipped into the trunk, locked inside, and sent to Timbuktu himself. Madame Adelaide's will is rewritten to exclude Edgar and include O'Malley and any future kittens he and Duchess have.
Madame also starts a charity foundation providing a home for all of Paris's stray cats. The grand opening which most of the major characters come, features Scat Cat's band, who perform a reprise of "Everybody Wants to Be a Cat".