God stopped killing people for "committing whoredom with the daughters of Moab" because "his wrath was turned away" by a man who thrust a javelin through a man of Israel and a daughter of Moab.

What was this man's name?

Phinehas

And when Phinehas, the son of Eleazar, the son of Aaron the priest, saw it, he rose up from among the congregation, and took a javelin in his hand;

And he went after the man of Israel into the tent, and thrust both of them through, the man of Israel, and the woman through her belly. So the plague was stayed from the children of Israel. Numbers 25:7-8