understudies
n. 预备演员,替角,代替之人( understudy的名词复数 )
An actor's or actress's understudy is the person who has learned their part in a play and can act the part if the actor or actress is ill.
He was an understudy to Charlie Chaplin on a tour of the USA.
他是查理·卓别麟美国巡演期间的替角儿。