Oh My Papa

 is a quest in Fallout: New Vegas.

Quick walkthrough

 * 1) (Optional) After completing Kings' Gambit, speak with Colonel Moore 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. (Completing this step first will give the added options of having the Great Khans join the NCR or killing Papa Khan for the NCR.)
 * 2) Go to Red Rock Canyon, enter the only non-tent building in the area called 'Great Khan Longhouse'
 * 3) You will see Regis, Papa Khan and Karl sitting and eating behind a long table.
 * 4) Talk to Papa Khan. Exhaust all chat options until a long sentence asking Papa Khan to abandon the alliance with Caesar's Legion appears. He will refuse regardless.
 * 5) Exhaust all chat options with Regis and Karl.
 * 6) 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.
 * 7) To obtain Regis' trust, you need to find him proof that the Legions make slaves of their allies. Stealing Karl's journal from his footlocker and using it to disgrace him in front of Papa Khan will gain you Regis' support at the same time (using Speech to disgrace Karl will leave you unable to use Karl's journal for Regis' support). Proof can also be found in Caesar's tent in his fort. It's a slave ledger that you will find on one of the tables in Caesar's tent.
 * 8) 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.
 * 9) To obtain Melissa's trust, simply visit her at the Great Khan Encampment and tell her that women aren't allowed to serve in the Legion.

NOTE: The fastest way to complete this quest, and get the Khans to ally with the NCR, is to follow steps 1-4, then: Done. 500 XP, Khan Fame gained, and the NCR have some "machette fodder" for the coming battle.
 * Exit the Longhouse, which triggers a conversation with Regis. Exhaust all conversation options, one of which will lead to Regis saying if Papa Khan was dead, he'd be the new leader, and would probably ally with the NCR.
 * Wait till night, run around behind the Longhouse and pick the Hard locked door to Papa Khan's bedroom. You can also pickpocket his room key by crouching behind him when he's seated at the table and after Karl is dealt with. Once inside, hide, then reverse-pickpocket a grenade or C-4 on him.
 * Find Regis in his tent and follow the conversation. His tent is located near the big fire with the brahmin. It has some skulls in front and a NCR-flag inside.
 * Talk with the Colonel at Hover Dam.

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 start with Colonel Moore, the quest series that ends with Kings' Gambit will need to be completed so that For the Republic, Part 2 will trigger. Otherwise, she'll just tell you to go away.

Alternatively, this quest can be triggered by simply entering The Great Khans' Longhouse in Red Rock, exhausting speech options with Papa Khan inside it, then leaving the longhouse to trigger the quest opening conversation with Regis.

Find Regis Evidence that Caesar will annihilate the Great Khans:

To convince Regis you need to give him a book called Legion slave ledger found in Caesar's tent at the The Fort. Stealing Karl's journal also works. Note that if Karl is disgraced through Speech, you will be unable to use his journal as evidence to gain Regis' support.

Convince Jack and Diane to speak out against Caesar:

You need to only convince 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.

Convince Melissa to speak out against Caesar:

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. *** If you have previously done the Don't Make a Beggar of Me Melissa will no longer be there to talk to, so make sure to do Oh My Papa first.*** PC ONLY: Use the console command "player.placeleveledactoratme 000E595C" to bring Melissa back and work around the bug (you will have to save, exit and restart the game to restore achievements on steam).

OPTIONAL: Find a way to disgrace Karl in front of Papa Kahn:

With high enough Speech (you'll need at least 75 to get through all 3 speech checks), 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. If you provide Papa Khan with Karl's journal, this will also convince Regis at the same time. Note that if Karl is disgraced through Speech, you will be unable to use his journal as evidence to gain Regis' support.

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.

Alternatively 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 Why Can't We Be Friends (assuming you haven't already completed it) quest and you will gain some infamy against the Great Khans (Unless you kill him without being detected). If you kill Papa Khan without being detected then talk to Regis, you will actually gain rep for the Great Khans.

Assassinating Papa Khan is probably the easiest solution to this mission, and can be done relatively easily, even with low sneak, assuming the player has a 75 lockpick skill(or you can wait around midnight and he`s going to walk straight from the table to his room, unlocking the door in the process). The rear door of the Longhouse leads directly to Papa Khan's bedroom, where he sleeps alone. Use a stealth boy (unless your sneak skill is high), pick the (hard) lock, and reverse-pickpocket a grenade onto the sleeping Papa. It sure beats slaughtering radscorpions and cazadores to get to Melissa, and you can do this without gaining Great Khan infamy. Also, this can be done even if Melissa's dialogue is bugged and doesn't require a trip to The Fort.

If you do not want to kill Papa Khan after talking to the Colonel, return to the long house and mention the treaty. Papa's concern for the Great Khans' legacy leads to two speech checks (both 75) and a longer third option (which eventually leads to the same two choices). Choosing the first speech check ("claim your own glory") will have the Khans fleeing Red Rock Canyon during the Battle of Hoover Dam (yielding Great Khans fame). The second speech check ("ghosts and martyrs") will prompt them to perform a suicide attack on the Legion at the dam. The third choice regarding past inspiration sends you to the Followers -- Julie Farkas at the Old Mormon Fort will point you toward a Follower named Ezekiel, who is located at 188 Trading Post. Ask him about the Khans and he will give you a history book, Pretty Pretty Horsies: A History of the Mongol Empire. If you deliver this book to Papa Khan with the kinder top dialog choice, the Khans will flee the canyon during the battle (Great Khans fame); delivering the book with the meaner dialog choice leads to the Khans' suicide mission.

Whether you've used speech or the book, you may finish the quest by wishing him the best (or not caring). However, if you ask him to ally with NCR and tell him to stick around, the quest will remain open for you to solve via talking to Regis/Colonel Moore and assassinating Papa Khan.

Behind the scenes

 * The title of the quest is a reference to Eddie Calvert's song of the same name. A well-known cover was made by Jim Nabors as Gomer Pyle.


 * The characters Jack and Diane are probably a reference to the 1982 song "Jack & Diane", by John "Cougar" Mellencamp.

Bugs

 * "Oh My Papa" Melissa glitch has been fixed in patch 1.02


 * If you trigger the dialogue where Papa refuses to break the alliance with the Legion BEFORE this quest is started, the option will NOT come back, as it seems to be a one time dialogue option, and so the quest gets locked and is unable to be completed because you cant trigger Regis coming up to you and making a proposal after you leave the Long House. For PC using the console command resetquest 00140c3a will bring back all of the dialogue options needed to trigger Regis although some of them may still be "grayed out" cycling through all of them normally will allow the encounter with Regis outside of the longhouse. For the 360, you can still get Regis to trigger his dialogue, but Papa Khans question will still never show up again. Amendment: If you go at night and/or when Regis is not sitting at the table and talk to Papa, Regis will not give you the dialogue necessary to start this quest.


 * Causing Karl to speak up as a part of his quest and then him being killed will result in "For the Republic, Part 2" to have the Great Khans as being eradicated when they are still there in Red Rock Canyon.
 * When Papa Khan is convinced that the Legion is not his allies all the Great Khans will turn hostile to Karl. If Karl is killed, which is most likely, it will result in "For the Republic, Part 2" to have the Great Khans as being eradicated when they are still there in Red Rock Canyon.


 * If you use speech on Karl you may not be able to use his journals as evidence to convince Regis. The best bet is to get Karl's Journal on his footlocker inside the longhouse BEFORE getting the quest (small karma loss, close the door to remain hidden) then, show it to Papa Khan
 * There seems to be a bug when starting this quest and leaving behind the backdoor (at least there was for me, patch 1.2). Then simply type "resetquest 00140c3a" in the console and talk again with Papa Khan and Regis. The Quest-Triggering dialogue-options are highlighted again.


 * A marker is not placed at Caesar's tent to get evidence for Regis, nor does Karl's journal complete objective. Confirmed. Karl's Journal is not the proper evidence to complete this quest on PC, Xbox 360(so far works fine on some 360 consoles) and the ps3 (correct you are looking for the Legion slave ledger, which can be found inside Caesar's tent at The Fort). There is a marker for the journal, however no new dialog appears. No marker is present for Caesar's tent and it appears the quest cannot be finished (this is NOT true. Althought the marker is missing, going to Caesar's tent and picking up the Legion slave ledger will update the quest as intended). However, on the 360, Karl's journal is inside the room next door to Papa Khan's, in a footlocker, and can easily be stolen.


 * If you don't get the speech option to assassinate Papa Khan from colonel Moore even if you have the Journal entry:"Talk to colonel Moore about a Great Khans/NCR alliance", just go into Papa Khan room's while he is sleeping around 1:00am and kill him (sniper rifle with noise suppressor mod is recommended) then find Regis and he will show you an speech option about the alliance, then go to colonel Moore an let her now about it, this way you will get the great khans support in the final battle