Actores fabulae means fictitious parties; fabulous or fictitious plaintiffs.
The following is a case law referring to actores fabulae:
When a lessee is merely the actores fabulae, and that by a fiction, the lessor is considered as being in fact the only plaintiff in a suit, nominal plaintiff is considered to be the real plaintiff, as in the case where the lessor of the plaintiff dies after judgment, the execution may issue in the name of the lessee, without the necessity of a scire facias. [Penn v. Klyne, 19 F. Cas. 166, 167 (C.C.D. Pa. 1817)].