Old Man

The Old Man is an NPC found outside the Dungeon. He guards the entrance, and the Dungeon cannot be fully explored until he is gone. When spoken to at day, he will tell you to return at night. When spoken to at night, he will give the player the option of fighting his master, Skeletron. He will deem players with less than 300 life (15 hearts) or 10 defense as not worthy, but still allows them to summon Skeletron.

When entering the dungeon without killing Skeletron, Dungeon Guardians will spawn and instantly kill the player.

The Old Man can only be hurt with lava. He will only take 1 damage per second from the lava. Killing the old man is pointless, because his death does not eliminate the Dungeon Guardians that will appear inside the dungeon. If he is slain this way, or the player fails to defeat Skeletron, the Old Man will return to the Dungeon during the next day.

When Skeletron is killed, the Old Man is freed from his curse and will arrive at your house as the Clothier. Thus, you can only fight Skeletron once per world as if you kill the Clothier a new one will spawn if a house is still available, not a new Old Man.