surrogate

A substitute (usually of a person, position or role).

A mixture of horseradish and mustard often serves as a surrogate for wasabi.

A person or animal that acts as a substitute for the social or pastoral role of another, such as a surrogate parent.

A deputy for a bishop in granting licences for marriage.

A politician or person of influence campaigning for a presidential candidate.

A judicial officer of limited jurisdiction, who administers matters of probate and interstate succession and, in some cases, adoptions.

Any of a range of Unicode codepoints which are used in pairs in UTF-16 to represent characters beyond the Basic Multilingual Plane.

An ersatz good.