(LifeWire) - A retirement plan custodian is a financial firm that is engaged to ensure that your retirement funds are kept separate from -- and are protected from -- your employer and your employer's creditors. Custodians also handle any necessary paperwork and tax reporting that your retirement plan generates.
A custodian is required for most qualified retirement accounts. These include employer-sponsored plans, such as 401(k)s, 403(b)s, SIMPLE IRAs and SEP IRAs; and personal accounts, such as traditional IRAs and Roth IRAs.
The custodian does not set the rules -- those are governed by the Internal Revenue Service and the account-creator's choices. The custodian simply ensures that they are followed.