to officially empower and authorize (someone) to act as a substitute in one's role or office
To act as a substitute for a person in their role or office
To officially empower, authorize, pronounce, and establish (someone) to be a deputy.
To act as an understudy (to someone).
To study or know a role to such an extent as to be able to replace the normal performer when required.
To act in a similar manner to some known person.
A performer who understudies; a standby.