Short answer. Yes. Where a defendant's identity or name is unknown, they may be sued under a designation such as unknown owner, heir, or devisee, or whatever description the case requires. Once the true identity is discovered, the plaintiff must amend the pleading to reflect it.
What the law says
Whenever the identity or name of a defendant is unknown, he may be sued as the unknown owner, heir, devisee, or by such other designation as the case may require; when his identity or true name is discovered, the pleading must be amended accordingly.
Rule 3, Section 14 — Unknown identity or name of defendant. Read the full provision →
Not knowing a name does not stop a case from being filed
The rule recognizes that a plaintiff sometimes has a genuine claim against someone whose real name is not yet known — property that was clearly taken or occupied by someone, for example, without a clear record of who. Rather than requiring the plaintiff to identify that person before filing anything, the rule allows suing them under a placeholder designation: the unknown owner, heir, devisee, or by such other designation as the case may require.
The designation has to fit the actual situation
The rule does not offer one single fixed label. It lists unknown owner, heir, devisee as examples, and then leaves room for such other designation as the case may require — the plaintiff has to choose a designation that genuinely describes the unidentified party's apparent relationship to the property or claim at issue, not simply attach a generic "John Doe" label without regard to the facts.
Amendment is mandatory once the identity surfaces
The placeholder is not meant to last indefinitely. The rule requires that when his identity or true name is discovered, the pleading must be amended accordingly. This is phrased as an obligation, not an option — once the plaintiff actually learns who the person is, the case has to be updated to name them properly rather than continuing against the unknown designation.
In practice this means the plaintiff has to keep working to identify the real defendant even after the case has already been filed under the placeholder name. Filing under an unknown designation is a way to get the case started, not a substitute for eventually naming the actual party who has to answer it.
Why this matters for a plaintiff without full information
Someone with a genuine claim should not be locked out of court simply because they cannot yet put a name to the person responsible. This rule lets the case start moving — preserving deadlines and getting the matter before the court — while the plaintiff works to identify the actual defendant, with the understanding that the pleading will need to be corrected once that identity becomes clear, and that service and other procedural steps still have to reach the real person eventually.