The Giant of Babil, a colossal killing machine built by Zemus, is the ultimate weapon of the Lunarians in Final Fantasy 4. When the eight crystals (the two sets of four Light and Dark cystals of Water, Fire, Earth and Wind) are gathered at the Tower of Babil, Zemus reaches out with his willpower to use the activate the tower's main function. The Tower transported the Giant to the Blue Planet from deep within the Red Moon. The Giant itself, a massive robot built to destroy the world as we know it, begins to rampage across the continent of Eblan. The corridors inside of the Giant serve as the Penultimate dungeon in the game. When the CPU found at the end is destroyed, the Giant falls and is left for dead.
In the DS remake of Final Fantasy 4, there is a hidden hyperboss called "Proto-Babil", which is a miniature version of the Giant of Babil. To fight it, you must use the item called "Dark Matter", which can be obtained by having Edge steal it from Zeromus.