A trustee is a person or entity designated by a person who creates a trust (grantor, settlor, or trustor) to manage and administer the trust for the benefit of the named beneficiary or beneficiaries. The trustee of a trust created for estate planning purposes is often the grantor, settlor, or trustor who created and funded the trust.

A trust agreement may designate one or more successor trustees who will become the trustee if the previous trustee dies, is unable to continue to serve as trustee, resigns as trustee, or is removed by court order following a lawsuit filed by the beneficiary or beneficiaries of the trust.

A trustee has a fiduciary duty to the beneficiary or beneficiaries of the trust. A fiduciary duty includes the highest duty of care (performance of duties under the terms of the trust agreement) and of loyalty (avoiding conflicts of interest) recognized in law.

In Washington State, a trustee is responsible for managing a trust in accordance with the terms set forth by the grantor (also known as settlor or trustor) and in the best interests of the beneficiaries. The trustee's role includes the prudent investment of trust assets, making distributions as specified by the trust document, and ensuring the trust complies with legal and tax requirements. Trustees in Washington are bound by the Washington Trust Act, which outlines the duties and powers of trustees, including the fiduciary duty to act with care, skill, and caution. This fiduciary duty is the highest standard of care in law, requiring trustees to act loyally and avoid conflicts of interest. If a trustee is unable to serve due to death, incapacity, resignation, or removal by the court, a successor trustee, as designated in the trust agreement, will take over the management of the trust. Beneficiaries have the right to hold trustees accountable and can bring legal action if they believe the trustee has breached their fiduciary duties.