Once they entered the Academy, Shikamaru and Chōji were among their classes' dead-lasts, along with Kiba Inuzuka and Naruto Uzumaki, spending their day pursuing more interesting pastimes. In Shikamaru's case, he would spend all day sleeping; to Shikamaru, even the very effort of putting pen-to-paper was just too much effort for him to put into it unless he had to. Iruka Umino, their instructor, would give them all the same condemnation.As a genin, Shikamaru Nara was the sort of unenthusiastic kid who liked to watch clouds. He preferred not to get involved in "troublesome" activities, pretending to be busy to avoid responsibility. He is fully aware of this side of his personality. He even named himself "the number one at running away" or "the number one coward". In fact, his most commonly used phrase is "how troublesome" in the Japanese version, and "what a drag" in the English version.

However, when duty calls, Shikamaru has a strong moral compass and sense of commitment to his comrades. Even though, by his own testimony, he lacks bravery, he will sacrifice himself and face almost certain death, for the sake of his friends and/or villagers without a second thought. Because of his raw leadership skill, he was the first genin from the Rookie Nine to become a chūnin. The weight of the decisions he must make as a chūnin and, thus, team leader have caused Shikamaru to mature rapidly. This was most evident after the death of Asuma. He vowed to protect and later mentor Asuma's unborn child, so that he could grow up to be a "cool adult" like Asuma. Shikamaru's sense of duty and commitment to the future of his village is also reflected in his willingness to enforce Konoha 11's recent decision to stop Sasuke at all costs, even in the face of potential objections on behalf of the original members of Team 7.Chōji Akimichi is Shikamaru's best friend. He respects and trusts him. He said that if he had to fight Chōji in the Chūnin Exams he would give up. After he left Chōji to fight Jirōbō, he told the rest of the team that Chōji is stronger than anyone else in this team.

Shikamaru loves to play thinking games that older men are usually into, such as shogi and go (His teacher, Asuma, even said at one point "That kid is like an old man. He likes to take things slowly"). He is a brilliant strategist. The Hokage often seeks his advice on defence strategies.[4] Although his former sensei, Asuma Sarutobi, often played against Shikamaru, Asuma had never actually managed to beat him. Asuma became suspicious upon realizing that Shikamaru was so good at board games, despite his abysmal grades. As a result, Asuma administered an IQ test disguised as a game to Shikamaru, which revealed that Shikamaru was beyond a genius, with an IQ of over 200. Sakura once states Shikamaru as being the smartest person in the Land of Fire.[5] During the Chūnin Exams, even the daimyō was impressed by his intelligence and offered him a position as his personal guard.