Atem has learned a great deal over the years, and every piece of information he’s learned or lived through has served to make him quite the multi-faceted character. Through his experience in Egypt he has picked up kindness, loyalty, and a calm level headed mind; as well as logic, strength and his ever appearing nobility. A King to his country, and a tried friend to all, he learned that ruling wasn’t as easy as his father made it look and he found strength from his friends and Sacred Court alike in trying to watch over his Kingdom.
Because of his connection with his people, he has a respect for all humans, even going as far as to claim he would destroy the class system when he became Pharaoh (shown when he was saved from a snake bite by Mahaad and subsequently sucked the poison out of his friend's arm). He felt that no man should be placed at a higher or lesser value than any other- and to this day that notion stands. As a spirit, he might have lost his way with it, and sometimes can appear very crass or cruel, but Yuugi has helped him back on his path. He is willing to give everyone a chance, though if someone persists to push their luck, they will get ousted very quickly. He is one who seeks redemption, not only for himself but for everyone.
However, if someone has done something terrible or awful in his eyes, he is likely to toss them aside and be done with them. If they pursue him after that they will get nothing but a cruel and cold attitude. This comes from dealing with people who have shown to be not who they appeared, and it is a sort of protective stance for him. Betrayal never comes easy, and if he feels someone is untrustworthy, he'll keep a very close eye on them.
Being locked away for three-thousand years took its toll on him quite harshly. In the beginning, when he was released as a spirit, he was quite insane and malicious. He often enjoyed in torturing people in something called a Yami no Game, and watching them burn. Though it should be noted that these games were not unwinnable. In fact, one of the greatest things people overlook is the fact that these games could easily be turned on their side if the player would realize it for what it was. Atem playing these games would pit the player against their greatest weakness. So it could almost be said that every time he played a game, he was looking for someone worthy, someone to finally beat the system (and by extension their own flaw) and prove him wrong. But, in essence, knowing how the human mind works, he really wasn't expecting anyone to. He was often extremely cruel, going so far as to paraphrase rules in order to get them to misunderstand. Some games didn't need paraphrasing and were simply unbelievably difficult on their own.
It took a long while after that for him to even out, but that insane attitude is easily surfaced when he is feeling isolated and backed into a corner (especially if completely without Yuugi to help him). It is at this point that he will lash out at anyone around him. For all he does shoving people away though, he has learned that friendship is something that is needed to exist in this world, and he perishes without it.
Because of this knowledge, he is friendly, most of the time- though very gauging. When he first will meet someone, the smile is there, but his brain is never turned off. He analyzes everything, usually to the point of fault. This is his greatest strength and weakness. His mind is always working, trying to figure things out, trying to work up a logical point for anything and anyone. When he thinks too much, he can actually become haughty and a know-it-all though once proven wrong he knows how to apologize. Even in knowing doesn’t make it any easier, though.
Atem is not usually easily provoked to anger, however if someone knows the right buttons, he flies off the handle rather quickly. He isn’t above lashing out and harming someone he has deemed as trouble. When given a situation where someone is insulting him or someone else, he’ll usually mark it off and retort with witty remarks, knowing that anger is what the other is looking for. However, if physical nature is brought into it, he will hesitate- if against himself, if he is witness to someone else being harmed, he will step in.
One of his greatest weakness is his almost non-ability to function on his own. He’s gotten so used to having friends, family, and loved ones by his side that when he is alone and realizes how lonely he is, he gets depressed. He is friendly by nature, and operates best with other people by his side. Though this is not to say that he can’t live alone. He can, and has done so for quite some time. But his preferred environment is with friends.
To people he has befriended, he is almost always seen as cheery, smiling, and happy around them. He retains quite a peaceful and calm way of mind most of the time, especially with those he likes. He's extremely loyal, and will risk himself to save others if necessary (as shown in Battle City when he jumped in front of Ra's attack without thinking to save Jonouchi and Mai). He is not self-serving (most of the time) and will always try to lend a helping hand to those in need. For all that he has seen, though, he recognizes that there is even more to do and learn, and through this he is always willing to go out and live life, to experience, and to have an adventure.
For everything he does know, Atem is very self-assured in a lot of ways. This becomes a problem sometimes as he can become very adamant about certain situations. When this happens, he's very hard to sway or budge, or get him to do anything really. If he feels he can get by on his own, he will, and won't press a situation any further; going as far as to abandon whatever it was that was upsetting him in the first place. Though this is seen in situations and with objects, it can be applied to people as well.
Atem is extremely smart, to the point of genius one might say, but he doesn’t flaunt it unless he’s feeling particularly arrogant. This is worsened sometimes by the fact that he has a very tall order of pride. He retains information and uses it against people if the situation calls for it, and he is an excellent strategist. This is how he had come by the title “King of Games”. Once learning the way a game operates, he is able to conquer it within mere hours of tinkering. It is an ability that comes naturally to him.