INTERCESSOR
mediator, go-between, intermediator, intermediary, intercessor
(noun) a negotiator who acts as a link between parties
Source: WordNet® 3.1
Etymology
Noun
intercessor (plural intercessors)
A person who intercedes; a mediator; one who reconciles enemies, or pleads for another.
A bishop who acts during a vacancy in a see.
Source: Wiktionary
In`ter*ces"sor, n. Etym: [L., a surety: cf. F. intercesseur.]
1. One who goes between, or intercedes; a mediator. (a) One who
interposes between parties at variance, with a view to reconcile
them. (b) One who pleads in behalf of another. Milton.
2. (Eccl.)
Definition: A bishop, who, during a vacancy of the see, administers the
bishopric till a successor is installed.
Source: Webster’s Unabridged Dictionary 1913 Edition