Albert Barnes Commentary Numbers 22:2

"And Balak the son of Zippor saw all that Israel had done to the Amorites." — Numbers 22:2 (ASV)

Balak the son of Zippor - The comparison of (Numbers 22:4) with (Numbers 21:26) suggests that Balak was not the hereditary king but a Midianite, and that a change of dynasty had taken place. His father’s name, Zippor, “Bird,” reminds us of those of other Midianites, e.g., Oreb, “Crow,” Zeeb, “Wolf.” Possibly the Midianite chieftains had taken advantage of the weakness of the Moabites after the Amorite victories to establish themselves as princes in the land.