Trinexx was an ancient being that came to be worshipped by the Lizalfos as their Deity of Natural Disasters.
Trinexx is a giant, turtle-like creature with a stone-like shell, with two additional heads protruding from its shell on either side.
Trinexx lived on Death Mountain in the Ancient Age. It is known that it came into contact with the Lizalfos at some point during this era, who were awed by Trinexx and came to worship it as a God.
As of 1 BG, Trinexx has not been seen in ages - it's most likely that it was dead or long gone.
The creature Grinexx is Trinexx's Lorulean counterpart in Termina. Grinexx is most likely a manifestation that has taken a form similar to Trinexx's.