Traditional enemies of the Israelites, the Edomites were the descendants of Esau who often battled the Jewish nation. Edom was in southeast Palestine, stretched from the Red Sea at Elath to the Dead Sea, and encompassed some of Israel's most fertile land. The Edomites attacked Israel under Saul's rulership. King David would later defeat the rogue nation, annexing their land. At the fall of the First Temple, the Edomites attacked Judah and looted the Temple, accelerating its destruction. The Edomites were later forcibly converted into Judaism by John Hyrcanus, and then became an active part of the Jewish people. Famous Edomites include Herod, who built the Second Temple.
Sources: Bridger, David. Ed. The New Jewish Encyclopedia. NY: Behrman House, Inc. 1976.
Schreiber, Mordecai (ed.). The Shengold Jewish Encyclopedia. Shengold Books. 1998.
Telushkin, Joseph. Jewish Literacy. William Morrow and Company, Inc. 1991.