The Amalekites were descendants of Esau through his wife Adah (Genesis 36:2, Genesis 36:16). One of Esau’s sons, Eliphaz, fathered Amalek through his concubine Timna (Genesis 36:12). They settled in the south of Canaan in the Negev (Numbers 13:29), and some also settled in the hill country of Ephraim (Judges 12:15).1
2 Thus says the LORD of hosts, ‘I have noted what Amalek did to Israel in opposing them on the way when they came up out of Egypt.