Britannica –
“According to Genesis, Amalek is a son of Esau’s son Eliphaz and of the concubine Timna, a Horite and sister of Lotan. Genesis refers to him as the “chief of Amalek” thus his name can be understood to be a title derived from that of the clan or territory over which he ruled. Indeed an extra–Biblical tradition recorded by Nachmanides relates that the Amalekites were not descended from the grandson of Esau but from a man named Amalek after whom this grandson was later named.
The Amalekites existed as early as the time of Abraham, in the region that would later become the Roman province of Arabia Petraea. This view corroborates Nachmanides’ claim of an origin for the Amalekites earlier than Esau’s grandson.”
“The Amalekites – members of an ancient nomadic tribe, or collection of tribes, described in the Old Testament as relentless enemies of Israel, even though they were closely related to Ephraim, one of the 12 tribes of Israel. The district over which they ranged was south of Judah and probably extended into northern Arabia. The Amalekites harassed the Hebrews during their Exodus from Egypt and attacked them at Rephidim near Mt. Sinai, where they were defeated by Joshua. They were among the nomadic raiders defeated by Gideon and were condemned to annihilation by Samuel. Their final defeat occurred in the time of Hezekiah.”
Encyclopaedia Britannica Online, http://www.britannica.com/EBchecked/topic/18343/Amalekites (accessed November 4, 2008)
“As the Jewish Encyclopedia put it, “David waged a sacred war of extermination against the Amalekites,” who may have subsequently disappeared from history. Long after, in the time of Hezekiah, five hundred Simeonites annihilated the last remnant “of the Amalekites that had escaped” on Mt. Seir, and settled in their place (1 Chr. 4:42–43).”
–The Book of Genesis 36:12 and 1 Chronicles (Jewish Tanach and Christian Old Testament). Accessed November 4, 2008