intermediary

That intermediates.

An agent acting as a mediator between sides to facilitate agreement or cooperation.

A Mr. Whymper, a solicitor living in Willingdon, had agreed to act as intermediary between Animal Farm and the outside world […]

White House chief strategist Steve Bannon has been in contact via intermediaries with Curtis Yarvin, Politico Magazine reported this week.

A person or organisation in an intermediate position (in a transaction, agreement, supply chain, etc.)

The intermediary between the manufacturer and retailer is the wholesaler

One or several stages of an event which occurs after the start and before the end.