Promiser
PROM'ISER, noun One who promises; one who engages, assures, stipulates or covenants. Fear, says Dryden, is a great promiser We may say that hope is a very liberal promiser
The import of a promise, when disputed, is not to be determined by the sense of the promiser nor by the expectations of the promisee.
[Note. In law language, promisor is used, but without necessity or advantage.]