The High Priest
The High Priest is considered the chiefest of all those who served at the temple. Aaron, the brother of Moses, was appointed as the first one by God. They were the head of the twenty-four courses that rotated serving in Jerusalem's temple. The division into courses occurred during the reign of King David. The office of any priest, filled by those of the tribe of Levi, represented the people before God.
For many years after the time of Moses the office of high priest was held based on heredity. It was considered a lifelong position. The Great Sanhedrin alone had the right to appoint, or confirm their appointment. In later times, however, civil authorities appropriated the right of appointment and filled the position based on their own religious and political considerations. For example, King Herod the Great (reigned 37 to 4 B.C.) appointed at least six of them, a frequent turnover that the New Testament may have hinted at (John 11:51).
There were qualifications for becoming High Priest other than heredity. The age of eligibility for the office is not fixed in the Bible, however, according to rabbinical tradition it was twenty years old (2Chronicles 31:17). Aristobulus III however, appointed by Herod the Great, was only 17 years old when he took the office. The man considered for the office also must be married and married only to an Israelite maiden (Leviticus 21:13 - 14). He was expected to be superior to all others in physique, in wisdom, in dignity, and in material wealth. In fact, if he was poor it was considered the duty of others who served in the temple to contribute enough money to make him rich!
The person serving in this most important position was considered the presiding officer of the Sanhedrin (supreme council of the Jews who met in Jerusalem). He was also the only one allowed to enter the Holy of Holies inside Jerusalem's temple, and that once a year, on the Day of Atonement (Yom Kippur - Leviticus 16). He was not permitted to come in contact with the bodies of the dead, not even of his own parents. He was not permitted, as a sign of mourning, to leave his hair disheveled, to expose it, or to rend his garments (see Leviticus 21, etc.).