noun
supporting actor; supporting actress
Refers to a performer in a supporting role in a film, play, or television production. Gender-neutral in Japanese, though English glosses may specify actor or actress.
彼はその映画で助演者として出演した。
He appeared in the movie as a supporting actor.
助演者賞を受賞した。
She won the award for best supporting actress.
脇役 is a more common and casual term for a supporting role or supporting actor, while 助演者 is slightly more formal and specifically refers to the person.
Compound of 助 (じょ, 'help, assist') + 演 (えん, 'perform') + 者 (しゃ, 'person').