The term Agagite is used in the Book of Esther as a description of Haman. The term is understood to be an ethnonym although nothing is known with certainty about the people designated by the name.
According to Cheyne and Black, this term is used to label Haman, figuratively, as a "descendant" of Agag, the enemy of Israel and king of the Amalekites. "Haman, as an Amalekite, is opposed to Mordecai, the descendant of Kish (Esth[er] 2:5) . . . The meaning is that there is an internecine struggle between the Jews and their enemies, like that between Saul and Agag of old."
A well known Midrashic explanation of the term relates it to King Agag of the Amalekites whereby it is viewed as meaning either a literal descendant of Agag or an antisemite, the Amalekites having come to be symbolic of the antithesis of Judaism.