Kraken

Legend holds that the kraken are descendants of three ancient tako emperors who were exiled by their own people for unspeakably evil acts.  During their exile, the tako emperors changed.  Corrupted by dark forces, they gained in size and malevolence, and wandered the sea destroying all in their path.  Where the original three kraken are, or if the even still exist, none know.  However all living kraken can trace their lineage back to those three.