Agag in the Bible Encyclopedia - ISBE

a'-gag ('aghagh, or 'aghagh, meaning unknown, possibly "violent," BDB): A name, or title, applied to the king of the Amalekites, like Abimelech in Philistia and Pharaoh in Egypt. It is used of two of these kings: (1) A king of Amalek, mentioned by Balaam (Nu 24:7) in his blessing of Israel; (2) A later king, in the days of King Saul (1 Sam 15). Saul was sent with his army to destroy the Amalekites, who had so violently opposed Israel in the Wilderness. He disregarded the Divine command, sparing the best of the spoil, and saving Agag the king alive (1 Sam 15:8,9). After rebuking Saul, Samuel had Agag put to death for all the atrocities committed by himself and his nation (1 Sam 15:32,33).

Link: https://bible-history.com/isbe/A/AGAG/