Whose remembrance is blotted out from under the skies that we are not to forget and why?

Answer From The Annual Reading Schedule - Week 47 Notes For Deuteronomy: Amaleq (Amalek) for attacking the back where the feeble ones were when Yisra'el (Israel) was tired and weary on the way out of Mitsrayim (Egypt) (Deuteronomy 25:17-19).