The “Executor” and the “Trustee” are similar in some ways, but very different in others.
An “Executor” only acts if someone has died. The Executor can be nominated by the deceased person, but that selection must be approved by the Probate Court. The Executor only has authority over property that passes under the Will, not property held in a Trust, property passing under a beneficiary form (like life insurance), or some forms of jointly owned property.
A “Trustee” is selected by you and need not be approved by the Probate Court. The Trustee handles all of the property in the Trust. Whereas an Executor only has authority after you die, a Trustee’s authority can exist during your lifetime, after your death, or both.