Oh My Papa

 is a quest in Fallout: New Vegas.

Quick walkthrough
1. Go to Red Rock Canyon, enter the only non-tent building in the area called 'Great Khan Longhouse'

2. You will see Regis, Papa Khan and Karl sitting and eating behind a long table.

3. Talk to Papa Khan. Exhaust all chat options until a long sentence asking Papa Khan to abandon the Alliance with Caesar's Legion. He will refuse regardless.

4. Exhaust all chat options with Regis and Karl.

5. Exit the Longhouse, Regis will speak to you about how to convince Papa Khan to ally with NCR instead of the Legion - obtaining the support of the 4 advisers (Regis, Jack, Diane and Melissa) & discrediting Karl.

6a. To obtain Regis' trust, you need to find him proof that the Legions make slaves of their allies.

6b & 6c. To obtain Jack & Diane's trust, you only need to convince one of them. Either pass a speech check of 60 with Jack or find Anders for Diane. He is in Cottonwood Cove, crucified at the entrance of town.

NOTE:

Killing Anders in Cottonwood Cove will cause you to fail this quest even if you haven't started it yet.

This quest may be broken if you have previously killed Motor-Runner. In a related quest given by Diane Aba Daba Honeymoon, you are to find Anders in Cottonwood Cove. If Motor Runner has been killed, you automatically fail that quest, and the discovery of Anders will not register as proof. To workaround, you must succeed the Speech check with Jack.

Detailed Walkthrough
Colonel Moore can be found at Hoover Dam. She will ask you to assassinate Papa Khan. You may accept the task, or reject it, and instead continue with a more diplomatic approach.

To convince Regis you need to give him a book called Legion slave ledger found in the Caesar's tent at the The Fort. Or by stealing "Karl's Journal" which is inside the Great Kahn's Longhouse

You need to only convince one of either Jack or Diane to complete their objective. They are located in the northwestern area of Red Rock Canyon, at a location marked Red Rock Drug Lab. Jack can be convinced via a Speech check. Diane requires evidence that Caesar is hurtful to drug runners. She can be convinced by finding Anders for her, in the side-quest Aba Daba Honeymoon.

Melissa is found in the western part of the Quarry Junction area, at a location marked Great Khan Encampment. Simply telling her that women are not allowed to serve in the Legion will convince her to speak against Caesar.

With high enough Speech, you can provoke Karl into revealing his true feelings about the Great Khans. Do this while inside the Great Khan Longhouse, with Papa Khan also present. You may alternatively tell Papa Khan about Karl's journal. Either way, the Great Khans will proceed to kill Karl, and the optional objective will be completed.

When you speak to Papa Khan after convincing the other Great Khans, you can pass one of two 75 Speech checks to convince him to break the alliance with Caesar's Legion.

Alternativly you can return to Colonel Moore after speaking to Regis and tell her that the Great Khans will help her if Regis is in command, she will then ask you to assassinate Papa Khan. Once you have killed him speak to Regis and he will tell you that he will break the alliance with Caesar's Legion and help the New California Republic. There is a downside to this option, you will instantly fail the Can't we be friends quest and you will gain some infamy against the Great Khans. If you kill Papa Khan without being detected (silent kill with a sniper rifle in his room at night) then talk to Regis you will actually gain rep for the Great Khans.

If you do not want to kill Papa Khan after talking to the Colonel,go back to the long house, and talk to Khan about the treaty. He will talk about wanting to leave a legacy. If your speech is at 75 or higher, you can talk him into accepting the treaty. If not, tell him you will help, and he will send you to speak with the doctor at the Old Mormon Fort. She will tell you about a wandering follower named Ezekiel, who is at 188 Trading Post. Talk to him, and he will give you a history book about the mongols. Take the book back to Papa Khan, tell him how the Khans can be like them. After he takes the book, choose the answer about him being wise and good luck, you"ll get some exp and build a good rep with the Khans.

Finally, head back to Hoover Dam and tell the Colonel the Khans will never be a problem again. She says good riddance, and that ends the quest with some good rep with NCR.

Bugs

 * If you use speech to discredit Karl or convince Papa once the four Khans agree to break away from Caesar, you will be unable to complete the mission, and For The Republic II, it will say you've killed all the Great Khans.
 * This may not be a bug, but the people of the Mojave considering the Khans "migrating" to be as good a solution as "exterminated".

If you're on console versions - Do not expect to advance any further in the mission, due to the impossibility of getting her to respawn.
 * The Great Khan encampment can be empty thus preventing you to get Melissa's approval. Îf That happens you can use the console through tapping ^ once than click on the ground while the console is open to target a location than type "PlaceAtReticle 000e595c" this will spawn melissa at the point you let her spawn.

The assumed cause for this is she has either been killed by the deathclaws nearby, or alternatively, if you have completed her quests before taking "Oh My Papa", she may have despawned. (Unconfirmed, need verification)


 * On pc version it does not place marker at The Fort, caesar's tent to get evidence for Regis. And Karls journal doesnt complete objective either.