mediator; go-between; middleman
A person who acts as an intermediary between two parties, often in negotiations, transactions, or disputes.
He brought the negotiations to a conclusion as a mediator between the two parties.
In real estate transactions, a middleman often steps in.
仲介者 specifically means a person who mediates between parties, while パイプ can figuratively refer to any person or means that serves as a connecting channel.
仲介者 is a neutral word for a go-between or mediator, whereas フィクサー implies solving problems through hidden influence, favors, or shady connections.
Compound of 仲介 (mediation) + 者 (person). The exact historical derivation is straightforward; the word follows a common pattern for agent nouns.