Short answer. As a rule, the injured person must sue in his own name. Every action must be prosecuted or defended in the name of the real party in interest — the one who stands to be benefited or injured by the judgment — unless a law or the Rules authorize someone else to sue.
What the law says
A real party in interest is the party who stands to be benefited or injured by the judgment in the suit, or the party entitled to the avails of the suit.
Rule 3, Section 2 — Parties in interest. Read the full provision →
What the law says
every action must be prosecuted or defended in the name of the real party in interest
Rule 3, Section 2 — Parties in interest. Read the full provision →
The real-party-in-interest rule
Rule 3 defines the proper plaintiff by stake, not by feeling: a real party in interest is the party who stands to be benefited or injured by the judgment in the suit, or the party entitled to the avails of the suit, and every action must be prosecuted or defended in the name of the real party in interest. Outrage, kinship and moral support do not create a cause of action. If the contract breached was your brother's, the land encroached on is your mother's, the debt unpaid is your cousin's — the judgment would benefit or bind them, and the case must be brought in their name.
Why courts police this at the threshold
The rule protects the defendant and the system as much as it channels the plaintiff. A defendant sued by the wrong person faces the prospect of winning or settling — and then being sued again by the person who actually held the right, because a judgment for or against a stranger to the right settles nothing. Requiring the real party in interest ensures the case is fought by the person whose rights are genuinely at stake and that its outcome actually ends the dispute. A complaint filed by someone without that stake invites dismissal before the merits are ever examined, wasting the very filing it took courage to make.
The exception the rule itself announces
The command opens with a hinge: unless otherwise authorized by law or these Rules. The name on the complaint must be the real party in interest's — except where a law or the Rules themselves permit another to prosecute. That is what makes suits possible for people who cannot practically sue alone: representation arrangements the Rules provide for, and statutes that confer standing on particular persons in particular situations. The point to hold onto is the direction of the exception — it exists only where the law grants it, and the person invoking it must be able to point to the authorization, not merely to the relationship.
What you can actually do for your relative
Being unable to sue in your own name does not mean being useless. You can help the injured relative get to a lawyer, gather the documents that prove the right — titles, contracts, receipts, correspondence — and shoulder costs. If the relative cannot act for themselves because of age, absence or incapacity, tell the lawyer exactly that: whether some form of representation is available, and in whose name the case must still be captioned, is precisely the kind of question the exception clause governs, and it turns on facts a lawyer must assess. What the rule forbids is only the shortcut — filing the case as if the wrong were yours.