Tortoiseshell is a coat color pattern, not a breed. A tortie's coat mixes black-based and orange-based colors in patches or a fine mottled blend, usually with little or no white; a cat with large white areas is called a calico instead. Dilute torties show soft gray and cream, and torbies add tabby stripes. Because the orange gene sits on the X chromosome, nearly all tortoiseshells are female, and the rare males usually carry an extra X chromosome.
Most tortoiseshells adopters meet are domestic shorthairs, though the pattern also appears in Persians, Maine Coons, British Shorthairs and many other breeds. Their reputation for tortitude is folklore rather than proven fact: an individual cat's history, age and socialization say far more about personality than coat color, and shelters have torties of every temperament.