The Eater is the only way to acquire Shadow Armor as it is the only Mob that drops Shadow Scales which are the only way to make all the demonite weapons except War Axe of The Night, Lights Bane, and Demon Bow. It is an essential part in advancing in the game as you will need the Nightmare Pickaxe to mine Hellstone to get the Molten Pickaxe to mine Cobalt Ore etc. It is the easiest boss to defeat for any character. The overall health is over 8000 but as it can only approach you 1-2 segments at a time. It is a Burrowing Mob so is immune to lava. The head should be avoided at any cost, even if it means going through the body or tail.
Weaknesses: Is weak because it can only attack 1-2 segments at a time, has low health and is more an endurance/dodging fight.
Strengths: Has over 8000 health overall, can surprise you from the ground, must be fought in The Corruption so has many other mobs to attack you.
How to Kill: Assuming you have at least an Iron Broadsword and about 2-5 defense. This is for Players who have early game equipment. If items such at the Sunfury, Excalibur, or Night's Edge were acquired this boss would go down in seconds.
Build an arena of about 30 blocks high out of wood platforms 10-20 blocks wide. When it spawns just stand by its side and swing your sword.