A Pharaoh is a king of ancient Egypt. Literally, the word "Pharoah" means "great house," and refers to the residence of the leader.
The first Pharaoh is mentioned when Abraham and Sarah are traveling through Canaan (Genesis 12:14-20). Abraham lied and told the Pharaoh that Sarah was his sister because he feared that Pharaoh would kill him in order to marry his wife. The Pharaoh does indeed desire Sarah for his wife, but becomes enraged that Abraham lied to him about his relation to her (Genesis 13:18).
The second Pharaoh is mentioned in Genesis 41:40 and 41:45. Joseph became viceroy to Pharaoh, and married his daughter Asenath.This Pharaoh had a good relationship with Jacob's family and invited them to live in the land of Egypt during the famine in Canaan.
The third Pharaoh (Exodus 1:8) "did not know Joseph." He embittered the lives of the Israelites, making them collect straw and forcing them to do much heavy manual labor. He announced a decree that the Hebrew male babies should be killed (Exodus 1:16).