Before the curse of the mallet and the tyrannical command of the lash, before Egypt grew into a horror house of bondage, there occurred a peculiar act of ignorance: “A new king arose over Egypt, who knew not Joseph.”
Whether this king indeed knew nothing of Joseph has long been a matter of some debate. Historically, it is possible that a new monarchy arose, on the heels of some war, perhaps, which held none of the old allegiances to Joseph and his family. Others argue that this “new” Pharaoh was well aware of how Joseph saved Egypt from economic collapse, but like many a dictator, Pharaoh feigned unfamiliarity whenever it suited him.
Rabbi Yehuda Hausman, “The Destruction of Memory”, Jewish Journal (1-7 January 2015), 42.