An executor holds his/her office as a trustee to the beneficiaries of the estate, and thus he/she is held to fiduciary duties.
In Williams on Wills, Volume 1, The Law of Wills, 8th Edition (London: Butterworths, 2002), page 225, author Sherrin, C. and others write:
"An executor is the person appointed by the will to administer the property of the testator and to carry into effect the provisions of the will.
"The ordinary method of appointing an executor is for the testator to name in his will a specific person to be his executor."
An executor is a personal representative.
A female executor is called an executrix.