Short answer. Any relative, friend, or other person acting on behalf of a resident incompetent who has no parent or lawful guardian may petition the court for the appointment of a general guardian over the person, the estate, or both. This rule governs incompetent adults; a separate 2003 rule governs minors.
What the law says
Any relative, friend, or other person on behalf of a resident minor or incompetent who has no parent or lawful guardian, or the minor himself if fourteen years of age or over, may petition the court having jurisdiction for the appointment of a general guardian for the person or estate, or both, of such minor or incompetent.
Rule 93, Section 1 — Who may petition for appointment of guardian for resident. Read the full provision →
The petitioner does not have to be a relative
The rule casts a wide net over who may bring the petition: any relative, friend, or other person acting on behalf of the incompetent may file it. There is no requirement of a family relationship — a concerned friend, or indeed any other interested person, has standing to petition just as a relative would, without needing to prove any blood tie at all to the incompetent adult in question.
The core condition: no parent or lawful guardian already in place
The petition is available where the incompetent has no parent or lawful guardian. If the incompetent adult already has someone lawfully serving in that role, this particular petition to appoint a new general guardian is not the applicable remedy — the absence of an existing parent or guardian already in place is what opens the door to filing.
This condition prevents the process from being used to displace a guardian who is already validly appointed and functioning in that same role for the exact same incompetent adult already.
Guardianship can cover the person, the estate, or both
The petition may seek appointment of a general guardian for the person or estate, or both, of the incompetent. This flexibility matters because an incompetent adult's needs may be entirely about who manages their finances and property, entirely about who makes personal and medical decisions for them, or genuinely both of these at once.
The petitioner should think carefully about which scope of authority the incompetent's actual situation calls for.
This rule is specifically for incompetent adults, not minors
A separate, later rule on the guardianship of minors now governs petitions where the ward is a minor, while guardianship of incompetents who are not minors remains governed by the Rules of Court described here. Anyone petitioning on behalf of an incompetent adult is on the right rule; a petition concerning a minor instead follows that separate, more recent rule.