A personal representative can be anyone who is legally recognized as having the authority to act on behalf of another person. This may be an attorney or other agent, but can be anyone the principal (the person being represented) or the court deems fit for the appointment.
Generally speaking, a personal representative is the executor of an estate, which is comprised of any real or personal property left behind when a person passes on.
A fiduciary is one type of personal representative. In a world and society in which such qualities and traits are becoming increasingly rare, a fiduciary must demonstrate that s/he is loyal, candid and honest, and will always act in good faith. This standard is known as punctilio honorum (poonc-TEE-lee-oh aw-NOH-room), or "point of honor."
The executor of an estate is one who deals with the legacy left behind by a deceased party. The duties of an executor include making payments and distributions to beneficiaries, collection of monies owed to the estate (for example, royalties for the use of intellectual properties) and the payment of any taxes owed on the estate.
A guardian is someone appointed by a person - or in some cases, the court - to act in loco parentis (ihn law-koh pah-REN-teese), or "in place of the parent." Essentially, the guardian assumes parental responsibilities for a minor child or children when both parents are deceased, or if the parents are found unfit to raise said children by a court of law.
A conservator is a person appointed by the court to manage the financial affairs of a person who is mentally or otherwise incapacitated, or is underage. For example, if a surviving parent dies as the result of an occupational disease leaving a minor child orphaned, and subsequently the estate is awarded a multi-million dollar settlement, a conservator may be appointed to manage said funds until the child reaches the age of twenty-one.