California Code, Labor Code - LAB § 5307.5

(a) Appoint a trustee or guardian ad litem to appear for and represent any minor or incompetent upon the terms and conditions which it deems proper.The guardian or trustee shall, if required by the appeals board, give a bond in the form and of the character required by law from a guardian appointed by a superior court and in the amount which the appeals board determines. The bond shall be approved by the appeals board, and the guardian or trustee shall not be discharged from liability until he or she files an account with the appeals board or with the superior court and the account is approved. The trustee or guardian shall receive the compensation for his or her services fixed and allowed by the appeals board or by the superior court.

(b) Provide for the joinder in the same proceeding of all persons interested therein, whether as employer, insurer, employee, dependent, creditor, or otherwise.