Moses
Numbers 25:8ESV·traditional attribution

and went after the man of Israel into the chamber and pierced both of them, the man of Israel and the woman through her belly. Thus the plague on the people of Israel was stopped.

Matthew Henry Presbyterian @wholebiblehenry

Here is a remarkable contest between wickedness and righteousness, which shall be most bold and resolute; and righteousness carries the day, as no doubt it will at last. I. Never was vice more daring than it was in Zimri, a prince of a chief house in the tribe of Simeon.

Commenting on Numbers 25:6-15

John Gill Reformed Baptist @doctorgill

And he went after the man of Israel into the tent,.... Into which he went with his harlot; the word here used is different from what is commonly used for a tent: Aben Ezra observes that in the Kedarene or Arabic language there is a word near to it, which Bochart, putting the article "al" to it, says (a), is "alkobba", from whence is the...

Jamieson-Fausset-Brown Reformed @jfbcommentary

the plague--some sudden and widespread mortality.