In Jewish folklore, Rahab or the "ruler of the sea" is the name of a water dragon or demon.
From the Hebrew 'rachav' lit. broad, large. Rahab is mentioned in the Talmud and the Old Testament, and means also noise, tumult and arrogance.
Rahab originally designated the primordial abyss, the water-dragon of darkness and chaos, comparable to Leviathan and Tiamat. Rahab later became a particular demon, inhabitant of the sea, especially associated with the Red Sea.
This name was also applied to Egypt, and the destruction of the Pharaoh after the Exodus of the Israelites from that country, was compared with the slaying of Rahab, perhaps a late corruption of Rahab slaying the Pharaoh (the Red Sea drowning his troops) (Isaiah 51:9-10). The difference between Rahab and Tannin is unclear in Jewish literature.
There have been several video game characters that have been named "Rahab" and have had characteristics of an underwater monster.