Bokrug, the Great Water Lizard, is a Great Old One. He was one of the many creations of H.P. Lovecraft and his Cthulhu Mythos.
Bokrug is massive, reptile-like god who dwell's in a lake that broders the cities of Ib and Sarnath. The citizens of Ib, the semi-amphibian Thuum'ha, worshipped the Great Water Lizard, and held an idol of him, known as the "Voicless One".
At some point the people of Sarnath, who were humans, slaughtered the Thuum'ha and stole the idol, which angered Bokrug.
Every year since that crime, there have been reports of stragne ripples over the otherwise placid lake. This until the one-thousandth anniversary of the destruction of Ib and it's people, after Bokrug rose from beneath the waters of the lake and punished the people of Sarnath for their ancestors crimes.
The Great Old One destroyed the city in such a vicious manner, that there were no ruins left. After this the Thuum'ha returned to Ib and have ever since lived undisturbed.