User blog comment:QuentinPlaysMC/The creature in the lost river and the "infection"/@comment-28224627-20160910125217/@comment-28436187-20160910164333

It was here before the precursors ( the Precursors come on the planet almost 1 000 years ago ) and this creature is called the " Grand Leviathan ". I'm not sure about that, but, I think it's an old cousin of the Sea Dragon, I read that on the last leak.