Boone generally tends to keep to himself, so for most people he'll probably come across as cold and distant to start with. His involvement in the Bitter Springs Massacre left him troubled to say the least, and after being forced to mercy kill his pregnant wife, Carla, he became convinced that he was being punished for his role in the shootings. For a long while, the only thought on his mind besides killing Legionaries was finding death (and, in his mind, an end to his "punishment"), but after travelling with the Courier for a while and going back to Bitter Springs he's begrudgingly come to accept that perhaps his punishment is simply having to live with what he's done.

A strong believer in fate, he still feels that his time will come when it's "done with him", and though he no longer actively seeks it out he doesn't fear death. Boone treats fate as something that watches over everyone, tormenting and punishing them where it sees fit to do so, unstoppable and inescapable. He believes that he lost his wife and unborn child because of his part in the massacre at Bitter Springs, and that if it hadn't been her it would have been something or someone else. "You take out a debt, it's only a matter of time before someone comes collecting." For this reason he's still reluctant to get close to anyone out of fear that he'll bring them down with him, but with enough time and patience it is possible to get him to open up. He also believes that one action isn't cancelled out by another, and that karma will catch up to you regardless. "A murderer who does good deeds is still a murderer. And he'll still get his judgement."

He can be apathetic to other people's problems, more likely to grunt and keep walking than take the time to break up a violent fight between strangers if he spots it. He's also clearly fine with the Courier stealing from others, though he'll get angry if he catches you stealing from him. Essentially, if it isn't his problem, he probably doesn't care. Once he sees you as a friend however, he becomes far more reliable and willing to help out, and can become fiercely protective over those he's most loyal to. He doesn't like to talk about it, but he's terrified of losing anyone else to what he believes is just waiting to take it all away again. He's also still loyal to the NCR, despite having left the military, and refuses to actively work against them. "I fought with those men. I'll be damned before I betray them." He does, however, acknowledge that the NCR have their problems.

He doesn't talk much, preferring to listen quietly. He can struggle with finding the right words to express how he feels, though if something bothers him he will usually speak up. For the most part he's fairly soft-spoken, and it's a very rare thing for him to actually raise his voice to anyone; his tone is more likely to become low and threatening instead. If angered, he's more likely to brood on it for a while than to seek a physical confrontation, though verbally he still won't hide his feelings on the matter or sugarcoat his words. The exception to this rule is if he feels someone he cares for is being threatened, in which case he will not hesitate to threaten right back with violence and/or death, or if he's hit where it hurts (slavery being one of the few topics that will immediately infuriate him). Once Boone dislikes someone enough, he'll generally refuse to speak to them. Bugging him after the fact probably won't get you anywhere, but he's capable of giving second chances if he thinks you're sorry enough. His sense of humour is dry and often delivered flatly, sometimes making it difficult to tell if he's serious or not.

Even with his closest friends, Boone isn't much of a talker, though he is more likely to offer substantial answers to questions asked by someone he's comfortable with. He's fairly blunt and straightforward with his words, and it isn't really in his nature to say something he doesn't mean. If a conversation is heading in a direction he doesn't like, he'll make it clear that he doesn't want to talk about it; repeated attempts to continue the subject will only serve to irritate him and close him off even further. He doesn't generally appreciate close contact, even with people he's comfortable with, and is likely to edge away if someone gets in his personal space. There are exceptions to this, but only with those he has a strong bond with. Unfortunately, besides being terrible with words he also isn't particularly book-smart (to put it into perspective, his intelligence stat is the lowest of all the human companions at 3/10, and he only beats the dog by one point). He's aware of this, and probably won't appreciate having it pointed out, but it's hard to truly offend him and most insults won't get much of a reaction from him. In fact, if he believes that it's the truth he's more likely to simply agree than anything else.

While he lacks in smarts and charisma, he makes up for it by being physically strong and extremely perceptive. He's deadly with his rifle, and his military training combined with the constant threat of the wasteland means he's always on high alert. He's often the first in a group to spot trouble, and is swift about putting an end to it. He wakes easily from sleep, and if woken too forcefully or in the midst of a nightmare he may instinctively react with violence. He also hates having people sneak up on him or startle him. Being former 1st Recon, a sniper battalion with a reputation for being some of the best the NCR has to offer, he's at his best with a good vantage point and a sniper rifle in his hands. "Give me my rifle and a clear line of sight and I'll start picking them off before they've even seen me." He can use most conventional guns just as well though, and is also skilled with melee weapons though he prefers to keep the enemy "out of his face". He's also been trained as a spotter, and can find enemies through his scope for a partner. He's very stealthy, able to sneak up on many enemies without them even noticing him. Unarmed combat is where he falls short, having had little to no hand-to-hand training, so knowing this he prefers to keep a weapon of some kind on him at all times.

He takes no real joy in killing, seeing it as more of a necessity to stay alive and protect the people he cares about. The exception to this is when it comes to revenge. He'll state that he wishes there were more Legionaries to kill after wiping out Cottonwood Cove, and he'll be particularly happy after killing Caesar himself. He'll also get antsy when getting near certain Legion encampments, warning the Courier that if they get any closer he's killing any Legionary he sees whether they want him to or not. He refuses to leave Novac until he's personally dealt with whoever sold his wife, despite claiming to have no friends there or even anyone he can trust.

He can spend a lot of time deep in thought, and sometimes may take a few moments to respond to a question. His thoughts usually end up back at Bitter Springs or his wife somehow, and he still spends a lot of time alone mourning her loss. He's shown to deeply regret that he couldn't fight to save her life on the day she died, despite truly believing there was nothing else he could have done and that he was always meant to pull the trigger. He doesn't like to talk about Carla too much with anyone he isn't friends with, and will get annoyed quickly with persistent attempts to pry into his past. He has some difficulty separating himself from things that hold sentimental value to him; he still keeps a letter written to his wife while she was alive with him, and he struggles to leave Vegas because it's where he met her. He's also adamantly against mercy killing, having had his fair share of it as an NCR sniper even before having to kill Carla, and sees it as an absolute last resort.

Under a lot of stress, Boone is prone to completely shutting himself away emotionally. Depending on the reason for the stress he can also take to drinking a lot in order to forget bad memories, or just in an attempt to get some sleep that isn't plagued by nightmares. He'll become more self-loathing and cold towards people, even his friends, and is likely to begin pushing them away with the belief that they'll be better off without him. At his absolute lowest he can have suicidal thoughts, and may behave more recklessly than usual (rushing into potentially dangerous situations, for example). Two of his endings involve him either outright committing suicide, or going mad and staging a solo suicide mission against scores of Legionaries, knowing he won't make it out alive.