What was the name of the Simeonite leader killed with a Midianite woman at Peor?

Answer: Zimri

The man was Zimri son of Salu, a Simeonite leader; the woman was Cozbi, daughter of the Midianite chief Zur.

“The name of the Israelite who was slain with the Midianite woman was Zimri son of Salu, the leader of a Simeonite family. And the name of the slain Midianite woman was Cozbi, the daughter of Zur, a tribal chief of a Midianite family.”— Numbers 25:14-15 (BSB)