Which king of Moab summoned Balaam to curse Israel?

Answer: Balak

Balak son of Zippor, king of Moab, feared Israel and sent messengers asking Balaam to come and curse them.

“So the Moabites said to the elders of Midian, “This horde will devour everything around us, as an ox licks up the grass of the field.” Since Balak son of Zippor was king of Moab at that time,”— Numbers 22:4 (BSB)