Background
Sakumo was a famous and powerful ninja of Konohagakure who, during his lifetime, held fame that was said to overshadow even that of the Sannin. His son, Kakashi, proved himself a genius like Sakumo and idolised him, desiring to become just as great a ninja as his father. His wife died when Kakashi was very young. Sakumo witnessed his son successfully passing the entrance exam to enter the Academy. Afterwards, he and Kakashi met Might Duy and his son Guy. Sakumo asked Guy to be friends with Kakashi in the Academy, Duy corrected Sakumo informing him that his son had failed the exam. As Kakashi began to openly question Guy's worth as a ninja with his weak aptitude for ninjutsu, Sakumo warned Kakashi to not underestimate Guy as he may someday grow stronger than Kakashi — noticing how arduously Guy trained to improve.
At some point in time during his career as a shinobi, Sakumo confronted and killed Sasori's parents, earning Chiyo's hatred.
While his son was still in the academy, Sakumo and his team were sent on a mission of great importance to Konoha. When his team-mates' lives were endangered, Sakumo chose to abandon the mission in order to save them. The impact of the mission's failure caused Sakumo to be vilified by the Land of Fire, the villagers of Konoha, and even those he had saved. Dishonoured, Sakumo fell into a deep depression, which caused his abilities to suffer as a result.