“Orochi (「ヤマタノオロチ」?; Yamata no Orochi) is a major demon of Ōkami and Ōkamiden. It is an eight-headed serpent demon that resides in the Moon Cave.” (Ōkami Official Complete Works, 2007)
“Serpent banished 100 years ago by Shiranui and Nagi.” (Ōkami)
Okami Wiki: Orochi