Dryad

The Dryad is an NPC that will move in to an empty house once you've killed a boss. The easiest boss to kill would be the Eye of Cthulhu or, if you have a flail weapon, the Eater of Worlds. The Dryad reveals in conversation that she is 500 years old. She's one of two female NPCs, the other being the Nurse.

The Dryad can tell you the percentage of Corruption vs Hallow in the world.

370px|leftThe Dryad does not drop any items upon death.

Quotes
"Whats this about having more 'bark' than bite?"

"So two goblins walk into a bar, and one says to the other, 'Want to get a Gobblet of beer?

"You must cleanse this world of its Corruption."

"The sands of time are flowing. And well, you are not aging very gracefully..."

"Be safe; Terraria needs you!"

"Have you seen the Old Man walking around the dungeon? He doesn't look well at all..." (Only when the Clothier is not present)

"It is a evil moon tonight. Be careful." (Only during Blood Moon)

"I wish that gun seller would stop talking to me, doesn't he realise I'm 500 years old?" (Only if Arms Dealer is present)

"That Merchant keeps trying to sell me an angel statue. Everyone knows that they don't do anything." (Only if Merchant is present)