Son of Elazar, grandson of Aharon.
At the end of Parshat Balak, the nation of Israel sin with women from Moav and Midyan in a place called Shittim. Israelite men sleep with these women who persuade them to worship their god Ba'al Peor. God punishes the people with a plague. At one point a prince from the tribe of Shimon - Zimri ben Salu - openly has relations with a Midianite woman. This infuriates Pinhas who runs them both through with a spear. As a reward for his zeal, Pinchas is granted God's covenant of peace. Pinhas leads a war of revenge against Midyan. According to the Midrash, Pinhas is one of the two spies Yehoshua sends to Yericho. After the tribes of Reuven, Gad, and half of Menashe return to their land on the eastern side of the Jordan River, they construct an altar which is interpreted by the western Israelites as a break with the nation and a forbidden act. Pinhas heads a delegation to confront the eastern community, and to threaten them with war if they do not remove the altar. The tribes answer that the altar they have built is not for sacrifices, but is a monument to their association with the rest of Israel (Jos. 22). Pinhas is mentioned as presiding over the Israelite army, instructing them via word of God to fight the tribe of Binyamin during the episode of Pilegesh Begivaa. If the same Pinhas is involved, the dramatic story must have taken place soon after the conquest of the land of Israel. Pinhas is an ancestor of Ezra. Another descendant of Pinhas, Gershom, is listed as accompanying Ezra from Babylonia to Israel.
(Courtesy of Rabbi Jonathan Mishkin)
For taking such a principled stand and for being ready to protect the nation of Israel from such immorality, Pinhas is rewarded with the charge of continuing to protect the Jewish people. That was the classic task of the Kohen; to educate the nation of Israel as to God’s laws and traditions, to serve as role models of service of God and to thereby protect the Jewish people from the danger and damage of immorality.
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