Definition of TESTATOR: (noun) / one who makes and executes a last will and testament, for example, if Tiffany has a will drafted and she executes the will, then Tiffany is referred to as the Testator. When Tiffany subsequently passes away, she is said to have died “testate”, or with a will.
The word "testatrix" used to be regularly applied as the female equivalent of "testator". It is less common today especially in the Surrogate's Courts of the 5 boroughs of New York City. Usage of the suffix "-trix" as applied to any word to indicate the female version is becoming increasingly outdated.