Part of the success of The Big Bang Theory is due to its fidelity to itself. It pays attention to its characters, and their interactions, and even their pasts, and adjusts accordingly. Penny (Kaley Cuoco) began the series as an airheaded neighbor, a bubbly blonde object of unattainable desire. But she quickly deepened as a character, showing sides of herself as both a frustrated wannabe actress and a sarcastic have-to-work waitress. Her on-again, off-again mating dance with neighbor Leonard (Joh