Bio
The Eye of Cthulhu is a pre-Hardmode boss. It is one of the first bosses a player may encounter, as it spawns automatically when a relatively early level of game advancement is achieved. It can also be summoned manually with the Suspicious Looking Eye at night (see Spawn below).

1. The Eye of Cthulhu has not yet been defeated in the current world.
2. At least one player in the world has at least 200 maximum health and more than 10 defense.
3. At least four town NPCs (including the Traveling Merchant and town pets) are present in the world.

Stage 1:
A good strategy in this phase is to aim mid-range weapons at the pupil of the Eye, since that is where it spawns the Servants. That way, you can kill the servants and damage the Eye. If you stand directly below the Eye and aim straight up with a piercing weapon, after a few seconds your projectile will fall back down and hit the Eye again. After spawning 3 or 4 Servants, the Eye will charge at you, attempting to ram you 3 times before hovering once more, so be prepared to evade. It turns rather slowly as it charges, giving you time to prepare your next dodge. It can be helpful to begin to evade after the 3rd servant is spawned, as this will often allow you to dodge its first charge.

Stage 2:
For the last half of the fight, the boss sheds its iris to reveal a fanged mouth. Make sure to take advantage of its transformation sequence as much as possible, since it just spins in place for a few moments and you can still damage it. It moves slightly faster and deals more damage when it hits you but it also has no defense. It will not be summoning any more servants, so this time it will simply keep rushing at you. When it does so, do not try to attack it - concentrate on dodging. It'll charge you 3 times, and then pause for a few seconds during which you can attack freely. Try to hit it with your strongest weapon. A viable, cheesy strategy in classic mode is to use the the slimy saddle once he starts spinning and attack him. The eye of Cthulhu will attempt to attack you but the slime mount will protect you from the teeth. In expert and master mode he can dash through so it will not work.