Ryūjin, which in some traditions is equivalent to Ōwatatsumi, was the tutelary deity of the sea in Japanese mythology. In many versions Ryūjin had the ability to transform into a human shape. Many believed the god had knowledge on medicine and many considered him as the bringer of rain and thunder, Ryūjin is also the patron god (ujigami) of several family groups.

Watatsumi , also pronounced Wadatsumi, is a legendary kami, Japanese dragon and tutelary water deity in Japanese mythology. Ōwatatsumi no kami is believed to be another name for the sea deity Ryūjin and also for the Watatsumi Sanjin , which rule the upper, middle and lower seas respectively and were created when Izanagi was washing himself of the dragons blood when he returned from Yomi, "the underworld".