This Shabbat we read פרשת זכור. It is really the only Shabbat of the year that there is a Torah obligation to hear the reading about עמלק.
We are commanded to remember Amalek and we must erase any remembrance of Amalek. The explanation here is that even though there is no more actual Amalek, as they were once known, what they represent, still exists. They are the epitome of pure evil in the world.
The Gemara in מסכת ראש השנה says that עמלק, שטן.