A supporting actor is an actor who performs roles in a play or film other than that of the leads.
These roles range from bit parts to secondary leads. They are sometimes but not necessarily character roles. A supporting actor must also use restraint not to upstage the main actor/actress in the play/movie. In earlier times these were often ethnic stereotypes. The title is usually specific to the performance, that is, a person may be a supporting actor in one film and the leading actor in the next. An individual who typically plays supporting roles is considered a character actor.
In television, a day player refers to most performers with supporting speaking roles hired on a daily basis without long-term contracts.
Supporting roles may be pivotal or vital to the story. In recognition of important nature of this work, the theater and film industries give separate awards to the Best Supporting Actor and actress. A supporting actor/actress can also be known as a 'sidekick'.