The Tavernkeep is an NPC that will show up in any layer of the world after the player has defeated the Eater of Worlds or the Brain of Cthulhu. He will appear as an unconscious man, and initiating a conversation with him will wake him. He can then move into any available valid housing.
The Tavernkeep sells the needed parts to summon the Old One's Army, the rest of his items (other than Ale) requiring Defender Medals dropped from the event.
"I've got the cure for what ails ya! Get it? Ale? No?"
"They say you're strong, well, I know strong. Let's see if you measure up."
"Back where I'm from, we only serve Root Beer..."
"This is a big upgrade from wiping that table all day."
"Life's a challenge when you're just naturally better than everyone else."
"What am I doing here..."
"A lot of tenacity and a little bit of luck can go a long way..."
"Have you seen any Meburs around here?"
"<Name of Dryad> seems nice. I should bring her back with me." (Only if Dryad is present.)
"Do you think <Name of Steampunker> has an extra of that gun? I know a witch that may want one." (Only if Steampunker is present.)
"No wonder <Name of Demolitionist> has so many accidents. You can't imagine how much ale he buys from me." (Only if Demolitionist is present.)
"Normally, I'm not much of a fan of Goblins, but <Name of Goblin Tinkerer> seems to be an alright sort." (Only if Goblin Tinkerer is present.)
"Anyone see where the Dryad went?" (Only during the day, if Dryad is present.)
"Really quiet out there. A little too quiet..." (Only during the night.)
"Check in with me, and do your job." (Only during the night.)
"You know, where I'm from, a Blood Moon is actually just an excuse to get some fresh air." (Only during a Blood Moon.)
"Moon Lord, don't you mean Abyss Lord?" (Only if Moon Lord has been defeated.)
"I know a Lavamancer that would really like that hellstone down in the underworld." (Only during hardmode.)
"Know any good places to set up shop? Would love to open up a bar here." (Only when he doesn't have a house yet.)
"Huh? How did I get here? The last thing I remember was a portal opening up in front of me..."
"We should really do something about the Old One's Army. Ask me about the Eternia Crystal if you want to learn more." (Before Tier 1.)
"Great job on fighting off the Old One's Army! But I'm sure we haven't seen the last of them, they didn't put up much of a fight this time." (After Tier 1.)
"The Army of the Old One's keeps getting stronger, yet you keep pushing them back! But something tells me they aren't quite finished with us yet." (After Tier 2.)
"You really kept the full force of the Old One's Army at bay? Maybe you should visit Etheria some time." (After Tier 3.)
First click on "Eternia Crystal" option:
For starters, take a few of these Defender Medals, on the house! I've got some special defenses you can purchase, but only with Defender Medals! (5 defender medals only given one time.)
Subsequent clicks loop these quotes in order:
"The first thing you need to know about are the special defensive artifacts I've got for sale, but only if you've got some Defender Medals!"
"You can use these artifacts to create traps and defensive towers. Doing so Consumes Etherian mana, a special energy dropped only by members of the Old One's Army!"
"Challenging the Old One's Army is rather simple. They are attracted to the power of Eternia Crystals, and that can be used to bait them out."
"To place an Eternia Crystal, you must obtain an Eternia Crystal and a stand to put in. It just so happens, you can buy em from me!"
"You'll want to place your Eternia Crystal stand in a pretty open, flat area. Lots of walls and stuff might make it pretty difficult to protect!"
"Once your stand is set up, just interact with it while holding an Eternia Crystal, and prepare for a fight!"
"Of course, you can't let the Old One's Army destroy the Eternia Crystal! This will have catastrophic consequences for my homeworld of Etheria!"
"You can place defenses at the cost of 10 Etherian mana. Once placed, the Eternia Crystal will release some of this mana. Otherwise, you will need to defeat enemies to get more."
"With the help of defenses, you will have to repel several waves of invaders who are attempting to destroy both you and the Eternia Crystal!"
"If you successfully repel the invasion, you'll be awarded more Defender Medals, which you can bring to me to purchase more artifacts and some other special rewards!"
"I've also heard rumors that the power of the artifacts themselves may be further unlocked if you defeat the Old One's Army. Perhaps you could even use them any time you wish!"
Occasionally, the Tavernkeep may hold a mug of ale in his hand, if the player just so happened to be next to the Tavernkeep and have a glass of ale in their hands, an effect will occur, suggesting a "toast". There is a chance that a 1-minute tipsy effect will be added to the player after toasting (untested).
One of the Tavernkeep's names, Moe, may be a reference to the bartender Moe Szyslak from the highly popular animated TV show The Simpsons.