Wisconsin Statutes Civil Procedure (Ch. 799 to 847) § 807.12. Suing by fictitious name or as unknown; partners' names unknown

(1) When the name or a part of the name of any defendant, or when any proper party defendant to an action to establish or enforce, redeem from or discharge a lien or claim to property is unknown to the plaintiff, such defendant may be designated a defendant by so much of the name as is known, or by a fictitious name, or as an unknown heir, representative, owner or person as the case may require, adding such description as may reasonably indicate the person intended. But no person whose title to or interest in land appears of record or who is in actual occupancy of land shall be proceeded against as an unknown owner.

(2) When the name of such defendant is ascertained the process, pleadings and all proceedings may be amended by an order directing the insertion of the true name instead of the designation employed.

(3) In an action against a partnership, if the names of the partners are unknown to the plaintiff, all proceedings may be in the partnership name until the names of the partners are ascertained, whereupon the process, pleadings and all proceedings shall be amended by order directing the insertion of such names.