Negotiator (noun)

A person who conducts negotiations; a mediator; a go-between.

Origin:

From late latin negotiator ("one who transacts business"), from negotium ("business, affair").

Examples:

1. The negotiator successfully brokered a deal between the two parties.
2. He is an experienced negotiator.
3. The negotiators worked hard to reach a compromise.
4. The team of negotiators arrived for the meeting.
5. The negotiator helped to resolve the dispute.