Considered to be the strongest Captain in the Gotei 13, Yamamoto is depicted as an old man with a long beard. There are many scars on his torso and head, suggesting numerous battles in his past. He wears the standard Shinigami Captain uniform, but its size is greatly exaggerated. He also drapes his haori over his back instead of actually wearing it. Despite his old age, he has a very muscular body. As the general of Gotei 13, Yamamoto is highly respected by many Shinigami, most notably Komamura Sajin, who views Yamamoto as a benefactor who saved his life. He has a fiery temper, and like fellow Captains Byakuya Kuchiki and Soi Fon, he believes that laws must be executed for the benefit of the community and despises those who break the rules. General Yamamoto founded the Shinigami Academy about 2000 years before the main Bleach storyline. Yamamoto was himself a teacher at this academy, and personally instructed Kyouraku and Ukitake. He admits to being rather proud of Ukitake and Kyouraku. When they became Captains, he "boasted about them as though they were his own sons." It has been revealed that he had ordered Urahara Kisuke to stabilize the Garganta gate so that Captains can pass through, and has sent 4 Captains so far to back up Ichigo's team.

Yamamoto's Zanpakutou is Ryuujin Jakka (Flowing Blade like Flame, Viz: Flowing Flame Blade). It is the oldest and most powerful fire-based Zanpakutou, and has greater attack power than all other Zanpakutou in the Soul Society. In sealed form, it is disguised as Yamamoto's staff, which disintegrates into a sword on command. Its Shikai command is "reduce the whole of creation to smoldering ashes." When released, Ryuujin Jakka and the area around Yamamoto is consumed in flame. The sheer power of the flame can disintegrate almost anything the sword is waved at. Only powerful fighters such as Kyouraku and Ukitake can resist it. Even in its Shikai, Ryuujin Jakka's power is enough to fight against two other Captains' Shikai simultaneously. His abilities as a Shinigami are no doubt powerful, as he was able to bring 8th Division Lieutenant Nanao Ise to her knees and immobilize her by looking at her and releasing his spiritual pressure. He was also able to fight on par with two of the most powerful Captains, Shunsui Kyouraku and Jūshirō Ukitake, for a decent period of time without any sign of injury, while they both came away with minor wounds.