The position of Kohein Hagadol, High Priest, is very fascinating. Aharon was the first Kohein Gadol, and he was followed by his son, Elazar.
This position was passed on from father to son, provided that they were worthy. Other than the Second Temple era, the High Priest did maintain very high personal standards.
In all of Jewish History, there was a little over 1300 years that the Temples or Mishkan were functioning. This means that there was about 300 years where this special role was abused. Shimon Hatzaddik was High Priest for forty years, and Yochanan served for eighty years during the Second Temple. The remaining 300 years had no less than 300 High Priests in that occupation. These were the ones who were unworthy.
During the thousand years that the Kohein Hagadol was fitting for his job, they fulfilled the requirements as explained in the Torah. They needed to be extremely righteous and holy, to be able to enter the Holy of Holies on Yom Kippur.
He was also qualified to wear the eight garments earmarked for him. Among them was the Choshen Mishpat, the breastplate. It contained the Urim Ve’tumim, that revealed G-d’s intentions in the world.
He needed to possess five special qualities. He needed to be handsome, wealthy, wise, possess physical strength, and be older in years.
The most important aspect of his position, was his officiating the Yom Kippur service. He was awake all night, and worked the entire day offering sacrifices. He uttered the holy Name of G-d, in order to achieve atonement for the Jewish people.
There is a description of the radiance of the face of the Kohein Hagadol as he successfully left the Holy Holies unscathed on Yom Kippur. May we merit seeing that radiant face in our lifetimes.