An actor is someone who plays characters in a film, television, radio, or theatre production. When most people think of actors they think of Hollywood superstars who perform in blockbuster films and this is often the ultimate aspiration of anyone dreaming of a career in acting. There are also stars within different fields of acting. For example there are well-known television and theatre stars in each discipline. It is difficult to achieve this degree of success in the field of acting, and the majority of actors perform in smaller productions, often starting in advertisements or as extras on television shows or films. There are many actors who make a successful career out of so-called bit parts and never have a starring role. Others, who achieve great success very early in their careers, become household names and get lots of major roles. The majority of actors will have a career that is somewhere between these two extremes.