Firelink Shrine, where the pool in front of the decrepit statue used to be. Kingseeker Frampt only appears after the Bells of Awakening have been rung.
Plot
Kingseeker Frampt appears in Firelink Shrine after the player rings both Bells of Awakening. He instructs the player to go to Anor Londo and obtain the Lordvessel. After the player obtains the Lordvessel, Frampt transports them to the entrance of the Kiln of the First Flame, and instructs the player to place the Lordvessel to gain access to the Kiln, and to ultimately kill Gwyn and prolong the Age of Fire.
Should the player give the Lordvessel to Kaathe instead, Frampt will become irate and leave the player for the rest of the playthrough.
Services
Kingseeker Frampt has the ability to consume items and break titanite into smaller pieces.
Feeding weapons and armor to him is not very profitable; most weapons only produce 50 Souls while most armor produces 100. Special weapons can produce much more, such as the Drake Sword, which results in 5,000.
When Frampt transports the player to the Firelink Altar, after retrieving the Lordvessel, it is not necessary to place it. By using a Homeward Bone or the Homeward miracle it is possible to exit and continue using Frampt's feeding service and at the same time interact with Kaathe and join the Darkwraiths. As long as the player does not place the Lordvessel, neither serpent will depart.
Dialogue
Click to see Dialogue (Contains Spoilers)
Snoring
Hmgg... Hmgg...
Introduction
Ahh, hello. Was it you who rang the Bell of Awakening? I am the primodial serpent, Kingseeker Frampt, close friend of the Great Lord Gwyn. Chosen Undead, who has rung the Bell of Awakening. I wish to elucidate your fate. Do you seek such enlightenment?
Introduction with Lordvessel
Ahh, hello. Was it you who rang the Bell of Awakening? I am the Primordial Serpent, Kingseeker Frampt, close friend of the Great Lord Gwyn. Chosen Undead, who has rung the Bell of Awakening. I wish to elucidate your fate, and the very reason your kind have appeared. Chosen Undead, your fate... is to succeed the Great Lord Gwyn. So that you may link the Fire, cast away the Dark, and undo the curse of the Undead. Now, let us take that vessel on a journey. I assume you are ready. Now, be still!
Answering "Yes"
Very well. Then I am pleased to share. Chosen Undead. Your fate... is to succeed the Great Lord Gwyn. So that you may link the Fire, cast away the Dark, and undo the curse of the Undead. To this end, you must visit Anor Londo, and acquire the Lordvessel.
Greetings
I am pleased to see you well. Is it something urgent?
Talk x1
Those who seek the Realm of Lords must brave Sen's Fortress, a deadly house of traps. Many have gone before you, but none have returned. Fate has chosen you, but proceed with caution.
Farewell
Farewell. Chosen Undead. I remain here, and await thee.
Waking Frampt up
...Hm? No, no, I'm fine, I'm fine. Well and wide awake! Do not treat me like an old withering snake.
Retrieving the Lordvessel
Heavens! You have done it! You have retrieved the Lordvessel! After a thousand years! It is you, it is really you! Hraaaoogggh! ... Forgive me. I really should calm down. Now, let us take that vessel on a journey. I assume you are ready. Now, be still!
Bringing the player to Firelink Altar
This is the Firelink Chamber, for the successor of Lord Gwyn. Now, place the Lordvessel on the altar.
Speaking before placing Lordvessel
What is it? Place the Lordvessel on the altar. No reason for pause at this point.
After placing Lordvessel
Very well. As Kingseeker, I shall now instruct you, the Lord's successor, in your next task. To achieve your fate, fill the vessel with powerful souls, commensurate to the great soul of Gwyn. Scarce few possess such brilliant souls. Gravelord Nito, the Witch of Izalith, the Four Kings of New Londo, who inherited the shards of Gwyn's soul... and Lord Gwyn's former confidant, Seath the Scaleless. All of their souls are required to satiate the Lordvessel. ... Are you ready? Then we shall return. Stay still for a moment!
Satiating the Lordvessel
Ahh...ohh! The Lordvessel is satiated... Magnificent... You are the righteous successor to Gwyn, the new Great Lord. And I am Kingseeker no more... Your acquaintance was an honour. I must admit, I am fond of you humans. May you enjoy your serendipity. And may the Age of Fire perpetuate.
Attacking him, jumping down without him, or giving Lordvessel to Kaathe
You sorry fool... You could not be the Chosen one. Enough... I shall slumber, until I am awakened again...
Trivia
Shortly after Frampt's arrival, the Crestfallen Warrior (who sits fairly close to it) complains about a horrible smell.[1] This is likely referring to Frampt. The Crestfallen Warrior will leave after being spoken to when Frampt is around, so keep that in mind before ringing the second bell of awakening.
In previous versions of the game there was a glitch where if a player jumped down the hole Frampt sticks his head out of, but quit and loaded before reaching the bottom, they would reach the Kiln of the First Flame. In doing so players could skip gathering the Lord Souls and go straight to the fight against Gwyn. This technique has been used for speedruns of the game.
If players have given Kaathe the Lordvessel already, then it is possible to prevent Frampt from leaving by rushing around and away from him. As long as he doesn't finish his dialogue, he won't disappear. Players can also prevent him finishing his dialogue by attacking him.
It's actually possible to kill Kingseeker Frampt, but only through the use of third party programs. Frampt has 11,120 HP and drops 5,000 souls after being killed.
Frampt will randomly be found sleeping deeply (usually after resting at a bonfire) even if he was spoken to only moments ago. He can be awoken by attacking him (kicking and punching are insufficient).
After ringing the first of the Bells of Awakening, Frampt can be heard snoring when passing through the flooded area of Firelink Shrine of which he will eventually emerge.
Removed Content
The following is content that is present within the code of Dark Souls, but not actually implemented in the game. Text was found from a text dump which can be found at: http://pastebin.com/hA42TwK8.
Click to see Removed Content
Some removed dialogue of Kingseeker Frampt suggests that he was supposed to be able to sell Humanity to the player.
Ahh, one other thing. You will require humanity to remain yourself while Undead. This I can provide you, but only in trade for souls.