interlocutor

interlocutor \in-ter-LOK-yuh-ter\, noun:

1. Someone who takes part in a conversation, often formally or officially.
2. The performer in a minstrel show who is placed midway between the end men and engages in banter with them.

In the course of an hour, Mukasey cracked jokes, asked an interlocutor not to address him with the honorary title "General" and continued to field questions even after his media director moved to get up from the table.
-- Carrie Johnson, "Highest Lawman Prepares to Meet Highest Court", Washington Post, March 22, 2008

Judge Richard Posner, of the appellate court in Chicago, has been the interlocutor for the contentious negotiations, which were raw with distrust on both sides, the sources said.
-- "Negotiators win time in Microsoft case", Business Report, March 28, 2000

The words promised excitement. I was going to be told something so confidential that my interlocutor not only didn't want to be named, but didn't want the information he was disclosing to be printed at all.
-- David Aaronovitch, "The Media Column: Why 'off the record' has to mean just that", Independent, May 21, 2002

Interlocutor is from Latin interlocutus, variant of interloqui "interrupt," from inter- "between" and loqui "speak."