Tortoiseshell is a coat pattern, not a breed. The coat mixes black-based and orange-based colors in patches or a fine mottled blend, usually with little or no white. Dilute torties look soft gray and cream, and torbies add tabby stripes. Nearly all tortoiseshells are female, because the orange gene sits on the X chromosome.
Most torties adopters meet are domestic shorthairs, though the pattern also shows up in Persians, Maine Coons, British Shorthairs and other breeds. The famous "tortitude" is folklore more than fact: a cat's age, history and socialization say far more about personality than color does. In a Springfield home, that means judging the cat in front of you, whether she's a bold climber or a quiet lap cat.