Who was Pinchas?

(יא) פִּינְחָס בֶּן אֶלְעָזָר בֶּן אַהֲרֹן הַכֹּהֵן הֵשִׁיב אֶת חֲמָתִי מֵעַל בְּנֵי יִשְׂרָאֵל בְּקַנְאוֹ אֶת קִנְאָתִי בְּתוֹכָם וְלֹא כִלִּיתִי אֶת בְּנֵי יִשְׂרָאֵל בְּקִנְאָתִי.

(11) ’Pinchas, the son of Eleazar, the son of Aaron the priest, has turned My anger away from the children of Israel by zealously avenging Me in their presence, and I did not destroy the children of Israel because of My zealous anger.

Rashi Numbers 25:11

"Pinchas, the son of Eleazar, the son of Aaron the priest": Because the tribes ridiculed him, saying, "Have you seen the descendant of Puti [i.e., Yisro], whose mother's father fattened calves for idol worship, and yet he killed a leader of one of the tribes of Israel?" Therefore, scripture traces his lineage to Aharon.

Aharon - Elisheva Yitro - Wife
Elazar - Wife
Pinchas

(ז) וַיַּרְא פִּינְחָס בֶּן אֶלְעָזָר בֶּן אַהֲרֹן הַכֹּהֵן וַיָּקָם מִתּוֹךְ הָעֵדָה וַיִּקַּח רֹמַח בְּיָדוֹ.

(7) And when Pinchas, the son of Eleazar, the son of Aaron the priest, saw it, he rose up from the midst of the congregation, and took a spear in his hand.

(ו) וְהִנֵּה אִישׁ מִבְּנֵי יִשְׂרָאֵל בָּא וַיַּקְרֵב אֶל אֶחָיו אֶת הַמִּדְיָנִית לְעֵינֵי מֹשֶׁה וּלְעֵינֵי כָּל עֲדַת בְּנֵי יִשְׂרָאֵל וְהֵמָּה בֹכִים פֶּתַח אֹהֶל מוֹעֵד.

(6) Then an Israelite man came and brought a Midainite woman to his brothers in full view of Moshe and the entire congregation, and they were weeping at the entrance of the Tabernacle.

Rashi Numbers 25:6

"And they were weeping": The law was concealed from him [i.e., from Moshe]. So they all burst out weeping. At the incident of the Golden Calf, Moshe stood up against six hundred thousand people... yet here he seemed helpless! However, [this was orchestrated] so that Pinchas could come and take [the reward] that he deserved