substitute; stand-in; understudy; double
Refers to a person who takes over a role, especially in theater, film, or performance, but also used more broadly for any temporary replacement.
The lead actor was ill, so the understudy went on stage.
急な欠員が出たので、彼が代役を務めた。
When someone suddenly couldn't make it, he filled in as a substitute.
He served as the understudy for the leading actress.
Due to a sudden illness, they had to bring in a substitute.
She was chosen as the understudy for the lead role.
The director is looking for a substitute for the actor.
代役 is a substitute performer or stand-in for a specific role (e.g. in film or theater), whereas 代行 covers any task or duty performed on someone's behalf, not just a performance role.
代役 refers to a substitute filling a specific role or duty (e.g. in a performance), whereas 代人 emphasizes the person who acts on someone else's behalf in general.