And a new king arose in Egypt who did not know Yosef. 1-8 --Rav and Shmuel [disagree over this point.] One said that he was a new king in the literal sense and the other said that he enacted new decrees as if he did not know of Yosef [and what he done to save Egypt.] - Rashi --
Both of these opinions are valid since he was born while Yosef was in prison and therefore was only a child during Yosefs reign and did not know much about him. Rabbeinu Bachya For any Egyptian, much less the Pharaoh himself, to forget Yosef and his enormous contributions to Egypt, defies all logic.
Yet, those familiar with Jewish history recognize this pattern all too well. First the Jews are greatly appreciated for their contributions to society and the economy, and then fear and jealousy sets in and they are viewed as dangerous subversives. There was no more loyal citizen than Yosef, yet in the end, it was all forgotten by the Egyptians. Only by retaining their Jewish identity did his descendants manage to transform their experience in Egypt into a positive one.