Golem

The Golem is a Hardmode boss. It is summoned by using a Lihzahrd Power Cell on the Lihzahrd Altar, which is found in the Lihzahrd.

Like many other bosses, the Golem has two stages. In its first stage, the Golem will shoot fireballs, extend its fists, and occasionally jump around. When the head reaches below half health, Golem will begin to shoot lasers.

Its second stage activates when it´s head has been "killed". Once this stage activates, the Golem's head will detach and fly around above its body, taking no damage and firing lasers at the player whilst they continue their fight with the body. In addition, its movement will speed up.

Trivia
The Golem might be a reference to Kaos Karnage from Donkey Kong Country 3: Dixie Kong's Double Trouble

This is currently the hardest boss in-game, but it also has the best loot.