(n.) One who makes peace by reconciling parties that are at variance.

adjudicator alleviative alleviator anodyne appeaser arbitrator assuager balm calmative conchie conciliator conscientious objector cushion diplomat dolorifuge dove family counselor go-between interceder intermediary intermediator lenitive make-peace marriage counselor mediator mitigator moderator modulator mollifier negotiator pacificator pacificist pacifier pacifist palliative peace lover peacekeeper peacemonger peacenik placater propitiator reconciler referee restraining hand salve sedative shock absorber smoother-over soother soothing syrup stabilizer temperer tranquilizer umpire wiser head