The Cyclops is an avatar in Ready Player One, which appeared at the beginning and final acts of the movie.
The Cyclops originally appeared in the 1958 movie called The 7th Voyage of Sinbad.
The Cyclops is a towering figure with the lower half of a hoofed animal, likely a sheep or goat, with brown fur, tanish-rock-like skin, a single eyes, three fingers on each hand, pointed ears and a single horns.
Role in Ready Player One
As Wade Watts/Parzival enters the OASIS, the Cyclops enters out of the entrance plaza, ducking down to enter said plaza, due to his height. In the final battle, also known as the Battle of Castle Anorak, the Cyclops appears at the front of the OASIS avatar crowd charging at the Sixers.
In the battle, the Cyclops is seen swing a club at the Sixers. In the end, the Cyclops, just like all of his OASIS peers were destroyed by The Cataclyst by Nolan Sorrento.