These are all roles that are found within a Trust
A Trustee is someone tasked with overseeing the assets held by a Trust. A Trustee must act in accordance with the Trust Deed (the document which established the Trust and outlines what its purpose and operations are). Trustees are often independent parties which helps when decisions are made about Trust assets.
A beneficiary is someone who benefits from the assets held by the Trust. The Trust deed outlines how the beneficiary might benefit.
A Settlor is the person who first provided the assets to the Trust, established the Trust Deed and selected the Trustees.
All Trustees, Beneficiaries and Settlors are named in the Trust Deed, which is the founding document of a Trust.