Oh My Papa

 is a quest in Fallout: New Vegas.

Quick walkthrough
Speaking to Regis in Red Rock Canyon about allying with the NCR is one way to start this quest. You must convince different members of the Great Khans to speak out against their alliance with Caesar's Legion, in order to convince Papa Khan to ally with the NCR.

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

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 Fortification Hill. Also, if you look in Karl's bedroom, you can get his journal and that will also convince Regis.

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.