A personal representative is appointed by a probate court judge to manage the administration of an estate when someone dies with or without a will and has not transferred all their property into a living trust. If the decedent had a last will and testament in which they named the person they wanted to serve as personal representative, the probate court judge will most likely honor his wishes and appoint this individual. The personal representative of an "intestate" estate, one without a valid will, is commonly called the estate's "administrator."
A trustee is named by an individual who creates a living trust. The person who creates a trust is called the grantor and are usually the initial trustee. The trustee manages property owned by the trust for the benefit of its beneficiaries.
Revocable trusts typically name successor trustees, someone to step in and assume control of the trust and its assets when the original trustee dies, or if he should become incapacitated to the point where he can no longer manage the trust or his own affairs.
Your estate will likely avoid probate and your heirs will not need a personal representative if you have a fully-funded living trust.