Arizona Killer

 is a quest in Fallout: New Vegas.

Quick walkthrough
Find and meet with Cato Hostilius. Assassinate President Kimball.

Detailed Walkthrough
Before you can do anything, you need to find and meet with Cato Hostilius. There is a glitch in the game, first, you are not told exactly where he is, and second, if you check the map before you leave Caesar's camp, then it will say that Cato is at the gate. First leave the camp, then check your map again. The easiest way to find Cato is to fast travel to Camp Forlorn Hope (an NCR camp), and head directly north for about 30 seconds. He's by himself with a makeshift bed next to him.