Mass. R. Dom. Rel. P. Rule 17
Parties Plaintiff and Defendant: Capacity
(a) Real Party in Interest. Except for any action brought under General Laws, chapter 152, section 15, every action shall be prosecuted in the name of the real party in interest. An executor, administrator, guardian, conservator, bailee, trustee of an express trust, a party with whom or in whose name a contract has been made for the benefit of another, or a party authorized by statute may sue in his own name without joining with him the party for whose benefit the action is brought; and when a statute so provides, an action for the use or benefit of another shall be brought in the name of the Commonwealth. An insurer who has paid all or part of a loss may sue in the name of the assured to whose rights it is subrogated. No action shall be dismissed on the ground that it is not prosecuted in the name of the real party in interest until a reasonable time has been allowed after objection for ratification of commencement of the action by, or joinder or substitution of, the real party in interest; and such ratification, joinder, or substitution shall have the same effect as if the action had been commenced in the name of the real party in interest. Identical to Mass.R.Civ.P. 17(a).
(b) Infant or Incompetent Persons. Whenever an infant or incompetent person, or an incapacitated person as defined in G.L. c.190B has a representative, such as a guardian, conservator, or other like fiduciary, the representative may sue or defend on behalf of the infant or incompetent person, or an incapacitated person as defined in G.L. c.190B. If an infant or incompetent person, or an incapacitated person as defined in G.L. c.190B does not have a duly appointed representative, he may sue by his next friend or by a guardian ad litem. The court may appoint a guardian ad litem for an infant or incompetent person, or an incapacitated person as defined in G.L. c.190B not otherwise represented in an action or may make such other order as it deems proper for the protection of the infant or incompetent person, or an incapacitated person as defined in G.L. c.190B.