substitute; proxy; representative; agent
Refers to a person who appears, acts, or handles a matter in place of someone else. Often overlaps with 代理人, which is the more explicit term for a legally or formally authorized agent.
Since my father was hospitalized, we had my brother act as his proxy to proceed with the paperwork.
If the person cannot attend, they may appoint a proxy.
彼は社長の代人として会議に出席した。
He attended the meeting as the president's representative.
I attended the meeting as the president's proxy.
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.
代表者 means a representative chosen to speak for a group or organization, while 代人 usually means someone substituting for one particular individual.
counter for people
A Sino-Japanese compound conventionally combining 代, 'substitution' or 'acting in place of,' with 人, 'person.'