Dual role
A dual role (also known as a double role) refers to one actor playing two roles in a single production. Dual roles (or a larger number of roles for an actor) may be deliberately written into a script, or may instead be a choice made during production, often due to a low budget. In film and television, dual roles are often used for comic effect, or to depict identical twins or relatives. In a theatrical production where more than one actor plays multiple characters, it is sometimes referred to as an "Ironman" cast.
Television[edit]
In television, soap operas have commonly used the technique to either portray twins (or even similar looking relatives), or to bring back an actor whose character has been killed. As an example, Denise Crosby's character, Tasha Yar is killed off in the first season of Star Trek: The Next Generation and another character was created to bring back Crosby in the third season.