Night beast

A fierce creature left as a guardian by the Massassi on Yavin 4 to protect their sacred temples. When an Imperial TIe fighter crashed into the Massassi ruins, the night beast emerged and ravaged the Rebel Alliance base. With the aid of the force and R2-D2, Luke Skywalker was able to lure the night beast into a Rebel transport and send it off the moon.

Source

 * ''A Guide to the Star Wars Universe