After Joseph saved Egypt from years of famine, this pharaoh favored Joseph. This pharaoh rewarded Joseph and allowed him to invite his family to join him and to live in Egypt.
By the time described in the Book of Exodus, this unnamed pharaoh had died. Generations of pharaohs had succeeded him to the throne of Egypt. Since neither pharaoh is named in Torah, the two different pharaohs are distinguish here by the book in which they appear.
- Wikipedia's article on pharaoh