Johnson was a soldier in the Enclave, serving as the squad marksman in Captain Judah Kreger's squad at Navarro with Orion Moreno, Doctor Henry, Daisy Whitman, and Gannon; he was known to often be in conflict with fellow squadmate Orion over their differing philosophies. Johnson hated the Enclave and everything they did; he often tried to subvert orders and "serve without serving." In contrast with Moreno, Johnson actually agrees with a lot of the NCR's goals and believes them to be the Mojave's best hope for a stable and free future.
Sometime after the destruction of Control station Enclave, the NCRsacked Navarro and he, the squad, Arcade Gannon's mother, and a young Arcade Gannon fled south into the NCR. They continued to flee east as Enclave personnel trying to integrate into the NCR were being found. He and the squad eventually settled in the Mojave Wasteland and went their separate ways. Johnson eventually settled down with a tribal girl he had met, but never had any children before she passed away. Now he sits alone in his cave, waiting for death to take him for the sins he'd committed while with the Enclave. He also reminisces about his former commander, Arch Dornan, saying "he was the meanest bastard [he] ever knew."
When asked about his nickname, he explains to the Courier that one day when he was surrounded by raiders and, out of options, he did the first thing that occurred to him: bite into the heart of one the raiders he had already taken down. This shock tactic caused some of the others to flee, and bought him the time he needed to kill the rest - and ever since the name has stuck, his improvisation growing into mystique.
For Auld Lang Syne: Cannibal Johnson is one of five Enclave remnants the Courier must recruit.
Effects of player's actions
During For Auld Lang Syne, if the player character encourages the Remnants to aid the Legion during the Second Battle of Hoover Dam, Johnson will refuse to participate in the attack and will leave the Remnants meeting in disgust. Unlike the similar scenario which occurs with Moreno if the player character encourages the Remnants to side with the NCR, Johnson cannot be convinced through any means to join the attack if the Legion is supported.
In addition to For Auld Lang Syne, Johnson will usually follow the Courier into the Legate's camp when fighting for an independent Vegas or NCR.
Attacking the brahmin in the camp will turn him hostile.
If one continues to talk to him about the Enclave, he will have a dialogue option about a drill sergeant who once caught a soldier without his uniform. This is a reference to Fallout 2 when the Chosen One travels to Navarro and talks to the drill sergeant there without wearing advanced power armor, Dornan will yell at him for being out of uniform.
Cannibal Johnson in the ending slides
↑The Courier: "What did you do when you were with the Enclave?" Cannibal Johnson: "Squad marksman. I'm pretty proud of the fact that I never killed a single soul who wasn't trying to kill me or one of my team first." (Cannibal Johnson's dialogue)
↑The Courier: "I'd like to know more about your former squad." Judah Kreger: "I was the officer in charge, and Johnson and Moreno were my heavy hitters. Henry handled tech things, and Whitman flew the chopper. Johnson and Moreno never got along, and I had my hands full keeping those two apart some days. It was a difference in philosophy, mostly. "Mercy" was not part of Moreno's vocabulary." (Judah Kreger's dialogue)
↑The Courier: "You make it sound like avoiding innocent deaths was uncommon in the Enclave." Cannibal Johnson: "I'm sorry to say that it was. Civilian casualties was acceptable and sometimes... encouraged. My former squadmate Moreno didn't need encouraging. Moreno and I might've killed each other if Captain Kreger hadn't been there to pull us apart." (Cannibal Johnson's dialogue)
↑Arcade Gannon: "If I had to pick anyone who didn't belong in the Enclave, it would definitely be Johnson. He hated what the Enclave was doing. Day to day, week to week, he would question orders, subvert mission objectives, do anything he could to serve without serving. It's amazing he was never court-martialed. He always had good things to say about my father. Said I was like him in a lot of ways. I wish I knew." (Arcade Gannon's dialogue)
↑Fallout: New Vegas Official Game Guide Collector's Edition p.361: "[3.11] Cannibal Johnson's Cave On the bluffs northwest of Camp Golf [3.23], close to Vault 34 [3.12], is a slit in the rocks above a steep gully, which sports a battered old door. Check the Hollowed-Out Rock at the entrance. Enter, and watch your step! Cannibal’s Chamber Deactivate the Bear Trap on the floor. Speak with Cannibal Johnson, and he greets you as an old friend. It’s only when you talk more that you realize he was hoping it was death. At this point, you can speak to him about “mean old” drill Sergeant Dornan, his time in the military, and whether he’s a Cannibal. He isn’t saying. But recalls a story where he bit the heart out of a Raider when he was surrounded. He also mentions his tribal wife, with pretty eyes. She’s dead a long time, now. Johnson's Coolhouse Cannibal Johnson looks like an accomplished hunter. There's also ground-water to drink, which is cleaner than it appears." (Fallout: New Vegas Official Game Guide Collector's Edition Tour of the Mojave Wasteland)
↑The Courier: "You live out here by yourself?" Cannibal Johnson: "Sure do. Had a wife for awhile - tribal girl, really pretty eyes - but she's been gone a long time now." (Cannibal Johnson's dialogue)
↑ 8.08.1The Courier: "Who's Sergeant Dornan?" Cannibal Johnson: "He was a drill instructor I knew. He was also the meanest bastard I've ever known. Once, he caught this private out of uniform and old Dornan went off on the most ear-blistering rant known to man. It was inspiring." (Cannibal Johnson's dialogue)
↑The Courier: "So, are you a cannibal?" Cannibal Johnson: "Ha. I'm not saying. It's part of my mystique, after all."
↑The Courier: "It sounds like there's an interesting story behind it." Cannibal Johnson: "[SUCCEEDED] The truth of it is that I did cut out a raider's heart, but only took a bite to mess with his buddies. They had me surrounded and I went with the first thing that came to mind. Some ran, and the rest were startled just long enough." (Cannibal Johnson's dialogue)
↑The Courier: ""Oh?"" Cannibal Johnson: "I've been in the Reaper's shadow for a long time now, and I thought he'd finally showed up to collect. He's just mocking me now." The Courier: "How much money do you owe this Reaper guy?" Cannibal Johnson: "What? I was talking about Death, kid. Guess that one went right over your head, didn't it? Old Sergeant Dornan would've had a field day with you." (Cannibal Johnson's dialogue)