Amalek עמלק

Amalek was the son of Elifaz son of Esav, from Timna (Bereishis 36:12). His descendants became the nation of Amalek.

Right after leaving Egypt, Amalek attacked the Jews at Refidim. Yehoshua led the battle, and when Moshe raised his hands the Jews prevailed (Shemos 17:8–13). 'Hashem is at war with Amalek from generation to generation' (17:16).

The Torah commands: 'Remember what Amalek did to you' and 'erase the memory of Amalek' (Devarim 25:17–19). King Shaul was commanded to destroy Amalek and spared King Agag (I Shmuel 15). Haman the Agagite descended from Agag.

Rashi brings the Midrash on 'who happened upon you on the way': Amalek 'cooled' the nations' fear of the Jews, like someone jumping into a boiling bath (Rashi on Devarim 25:18). Parshas Zachor is read on the Shabbos before Purim.