A good question. And the answer is quite simple.
As used in estate planning law, the terms "Settlor", "Trustor" and "Trustmaker" are all interchangeable. They all refer to the person who created the Trust.
Some practitioners also use the term "Transferor", "Donor" or "Grantor", since the person setting up the Trust transfers (or donates, or grants) assets to the Trust.
In our practice, we prefer the term "Settlor" just because it's the term most commonly used in the California Probate Code.
[For information only; may NOT be relied upon as legal advice.]