Numbers 16:1 - Albert Barnes' Notes on the Bible

Amram and Izhar were brothers (compare Exodus 6:18), and thus Korah, the “son,” i. e. descendant of Izhar, was connected by distant cousinship with Moses and Aaron. Though being a Kohathite, he was of that division of the Levites which had the most honorable charge, yet as Elizaphan, who had been made “chief of the families of the Kohathites” Numbers 3:30, belonged to the youngest branch descended from Uzziel Numbers 3:27, Korah probably regarded himself as injured; and therefore took the lead in this rebellion. Of the others, On is not again mentioned. He probably withdrew from the conspiracy. Dathan, Abiram, and On were Reubenites; and were probably discontented because the birthright had been taken away from their ancestor Genesis 49:3, and with it the primacy of their own tribe among the tribes of Israel. The Reubenites encamped near to the Kohathites (compare Numbers 2:25 and plan), and thus the two families were conveniently situated for taking counsel together. One pretext of the insurrection probably was to assert the rights of primogeniture - on the part of the Reubenites against Moses, on the part of Korah against the appointment of Uzziel.