ERISA Section 401(a) Named Fiduciary 

A 402(a) Named Fiduciary is designated in the plan document as having the overall authority to control and manage the operation and administration of the plan. Most commonly, the Named Fiduciary is the ERISA section 3(16) Administrator. 

ERISA Section 3(16) Administrator 

A 3(16) Administrator is the person or entity "so designated" in the plan document. The employer is the default Plan Administrator if none is designated. The Plan Administrator is basically responsible for any fiduciary responsibility not assumed by the ERISA section 403(a) Trustee.

ERISA Section 403(a) Trustee 

A 403(a) Trustee is named in a 401k plan or trust document and has exclusive authority and discretion to manage and control plan assets.

ERISA Section 3(38) "Investment Manager

A 3(38) Advisor is a type of financial advisor that assumes sole fiduciary liability for investment selection and monitoring. When an Investment Manager is hired, the Trustee is not responsible for plan assets controlled by the Investment Manager. An Investment Manager must be a bank, an insurance company, or an RIA subject to the Investment Advisers Act of 1940.

ERISA Section 403(a)(1) "Directed Trustee"

A “Directed Trustee” is a type of trustee that lacks the discretion of a full 403(a) Trustee. A Directed Trustee holds plan assets, but does not control them – they are subject to the direction of the Named Fiduciary in accordance with the terms of the plan document and ERISA.