Who is Bokrug from Dagon and Other Macabre Tales and what is their importance?

Bokrug, the water lizard god, is a character in The Doom that came to Sarnath. He is worshipped the inhabitants of Ib. After Ib is destroyed, the Bokrug is taken to Sarnath where he arises from the lake 1,000 years later and destroys Sarnath.