Kolossus (known as Kolosse in French) is the largest monster in Code Lyoko. It has only appeared in the Ice Sector and the Ice Sector Replika. The Kolossus appears in Cold Sweat where it almost destroys the Skid. During Down To Earth, it destroys the Skid in a single hit.
The Kolossus has four Eyes of X.A.N.A., however it is the large Eye of X.A.N.A. on its face and the one on its sword that must be hit to kill it. Hitting any of the large Eyes individually does nothing to the Kolossus, as shown when Yumi threw a fan at the Eye of X.A.N.A. on its face. The fan was seemingly destroyed and the Kolossus seemed unhindered by the attack. However, when Ulrich stabbed the Eye and kept his weapon there, the Kolossus was paralysed until X.A.N.A. drew energy from all the Replikas to help the Kolossus. Hitting any of the small Eyes on the sword makes the Kolossus halt for a short period of time.
If the Kolossus touches a Tower, the part of the Tower that the Kolossus is touching glows red - possibly because of the seemingly intense heat on its hands. The Kolossus destroys the Skid in Down to Earth by knocking it off the Tower it was connected to, making it crash in to the Digital Sea. The Kolossus was defeated by Ulrich, who was devirtualised soon after by the monster's corpse, which crushed him.
The monster's name was given by Odd in Cold Sweat. He spells it with "K" so it's sounds like K.O., although he's not sure who will get K.O.-ed.
Ulrich is the only one so far to eliminate the Kolossus, by stabbing it in both of its Eyes of X.A.N.A. (one on its head, and one on its sword arm).
Odd once called the Kolossus "King Kong", in Down to Earth.
Odd also called the Kolossus "the Heap" in the same episode.
The creation of the Kolossus is a giant catalyst in the final episodes of the 4th Season.
Revealing the number of Replikas made Jeremie think twice about the idea of destroying Replikas one by one.
Destruction of the Skid further convinced Jeremie to build the X.A.N.A. Destruction Program.
The Kolossus has only appeared in Ice-related areas (the Ice Sector and its Replika).
Kolossus appear as final boss in Code Lyoko DS: Fall of X.A.N.A.
Kolossus in front of the Skid.
It's sword-like arm has the Eye of X.A.N.A. on it; three small ones and one larger one.
Steam can be seen coming out from the monster.
The Kolossus smashes down onto the ice after being stopped by Jeremie.
Ulrich staps the giant right in it's eye, paralyzing it for only seconds.
X.A.N.A.-William can be seen standing on it's shoulder.
X.A.N.A. William watches from the safety of the giant beast.
The Kolossus slowly stomps through the Ice Sector.
The Kolossus has been taken down by Ulrich.
The large Eye glows after being hit.
Ulrich fights X.A.N.A.-William while on the Kolossus.
It emerges from the Ice Sector water.
Mantas aid the Kolossus as it roams the Ice Sector.
It heads straight for the tower.
Close up of the Kolossus.
Jeremy sees the Kolossus on the factory interface.
Ulrich and Aelita trying to run from the Kolossus.
Ulrich and Aelita meeting the Kolossus.
The Kolossus in Fall of X.A.N.A.