The Big Bang Theory originally centred on five characters living in Pasadena, California: Leonard Hofstadter and Sheldon Cooper, both physicists at Caltech who share an apartment; Penny, a waitress and aspiring actress who lives across the hall; and Leonard and Sheldon's similarly geeky and socially awkward friends and colleagues, aerospace engineer Howard Wolowitz and astrophysicist Raj Koothrappali.
