My father recently passed away in Sioux Falls and I've been appointed Personal Representative of his estate. What is a "fiduciary duty" in South Dakota?

In South Dakota, a Personal Representative is a "fiduciary" who (except as otherwise provided in the will) must observe the standards of care in dealing with the estate's assets that would be observed by a prudent person dealing with the property of another.

A "fiduciary duty" exists when an individual places the utmost trust and confidence in another person to manage and protect property or money.  In other words, the "fiduciary" has an obligation to act for another's benefit.