1) Agent 2) Compromiser 3) Diplomat 4) Holdout 5) Intercessor 6) Intermediary 7) Intermediator 8) Judge 9) Manager 10) Mediator 11) Mediatorial 12) Negotiant 13) Negotiatress 14) Negotiatrix 15) Treater 1) Arbitrator 2) Bargainer 3) Communicator 4) Diplomat 5) Go-between 6) Hostage film hero 7) Intermediary 8) Mediator 9) Negotiant 10) Someone who negotiates 11) Treater 12) Union intermediary 
A negotiator is a person who engages in negotiation. Negotiator may also refer to: ...
• (n.) One who negotiates; a person who treats with others, either as principal or agent, in respect to purchase and sale, or public compacts. • (n.) One who negotiates; a person who treats with others, either as principal or agent, in respect to purchase and sale, or public compacts.
Ne·go'ti·a`tor noun [ Latin : confer French négociateur .] One who negotiates; a person who treats with others, either as principal or agent, in respect to purchase and sale, or public compacts. 
[n] - someone who negotiates (confers with others in order to reach a settlement)
negotiant noun someone who negotiates (confers with others in order to reach a settlement)