A Complex Trust is not a Simple Trust and is able to accumulate income, distribute amounts other than current income, and make payments for charitable purposes. Generally, a complex trust would provide its own withholding certificate in its own name, as it is not treated as a flow-through entity.
Citations: Treas. Reg. § 1.1441-1 – Requirement for the deduction and withholding of tax on payments to foreign persons. Treas. Reg. § 1.1441-5 – Withholding on payments to partnerships, trusts, and estates.