John Gill Commentary Genesis 36:30

"chief Dishon, chief Ezer, chief Dishan: these are the chiefs that came of the Horites, according to their chiefs in the land of Seir." — Genesis 36:30 (ASV)

These [are] the dukes [that came] of Hori The ancestor of Seir, from which he is called the Horite, unless the singular is put for the plural, used in (Genesis 36:29): among their dukes in the land of Seir; not that there were other dukes besides them in the land of Seir until Esau got among them, but these were they whose habitations were before in the land of Gabla (or Seir); as the Targum of Jonathan paraphrases it; or "in", or "according to their dukedoms", as the Septuagint version; in their respective families where they had the government, and which became very numerous.