Kuma was once an abandoned cub in the forests of the Mishima estate, but was saved when Heihachi Mishima discovered him and took him in as his pet. Heihachi taught Kuma simple commands, which Kuma picked up at an alarming rate. After two years, Heihachi began to see Kuma's true potential, and so he began training him in the arts of Kuma Shinken, a martial art Heihachi designed specifically for Kuma. Wishing to test out Kuma's strength, Heihachi entered him in The King of Iron Fist Tournament.
In the previous King of Iron Fist Tournament, Kuma was defeated by Paul Phoenix, and Heihachi was defeated by Kazuya Mishima. Kuma's fighting techniques had began to decline preceding the first tournament due to him becoming complacent and lazy, and so he resolved to train harder to defeat Paul Phoenix when they meet next. After Heihachi's loss to Kazuya, Kuma and Heihachi retreated into a mountain dojo to begin training once more. Kuma entered The King of Iron Fist Tournament 2 with his master, vowing to destroy Paul Phoenix during the tournament.
During Kuma's travels with Heihachi, Kuma died of old age. Before he passed away, he had a cub, which was also named Kuma by Heihachi, perhaps in homage of beloved first pet. Eventually, Kuma II became Heihachi's pet, and Heihachi trained him in Kuma Shinken, as he did Kuma II's father years ago.
Kuma II is more intelligent than his father, but is also lazier. One day, while he was immersed in a television show, Kuma suddenly went wild at the sight of a Martial Artist with a scarlet go-gi. The fighter was the original Kuma's old rival, Paul Phoenix. Since that day, Kuma trained intensely in order to defeat Paul in battle. Not interested in defeating Ogre, the fighting God, Kuma enters The King of Iron Fist Tournament 3 with the sole intention of defeating Paul Phoenix.
During the previous tournament, Kuma lost to Paul Phoenix. Kuma realized that he had lost touch with his animal roots, and that as long as he remained Heihachi's pet, he would be restricted in harnessing the power of his natural power and instincts. Determined to revive his animal instincts, Kuma began training in the mountains of Hokkaido, and for the first time in his life, he trained alone, without Heihachi.
While training, Kuma found life in the wilderness more intense than anything Kuma went through with Heihachi. Despite this, Kuma continued his training, and felt his skills improving, and even developing his own attacks. Although he had made some massive strides in his life to revive his animal instincts, Kuma kept one quirk - he could not live without television. He would frequently go down to nearby villages to watch TV through the windows of the villagers' houses. One day, Kuma went down to the villages to watch some TV, as per usual, but when he looked through the window of one house, he saw a commercial announcing The King of Iron Fist Tournament 4. With his animal instincts raging, Kuma headed to the tournament, once again, with the sole intention of defeating Paul Phoenix.
Kuma had finally accomplished his goal of defeating Paul Phoenix during The King of Iron Fist Tournament 4. However, Kuma's jubilation was brought to an abrupt end when he found that his master, Heihachi, had died. Kuma lived in sorrow after his beloved master had died, but upon seeing the uncertainty surrounding the Mishima Zaibatsu, Kuma decided that saving the Mishima Zaibatsu would be the perfect way to demonstrate his loyalty to his late master.
However, the chaos at the Mishima Zaibatsu had already subsided when Kuma arrived, and he was escorted out of the building by security, giving Kuma no choice but to return to the wilderness. After the Mishima Zaibatsu announced The King of Iron Fist Tournament 5, Kuma decided he would enter the tournament, and take the Mishima Zaibatsu in honor of Heihachi.
During the previous tournament, Kuma believed that no one could rescue the Mishima Zaibatsu from its captor. Kuma was determined to do just that, and so he confronted the Zaibatsu. However, the Zaibatsi's new CEO, Jin Kazama, was ready for him, and easily defeated Kuma. Kuma was discared in the Hokkaido wilderness once again. Although he was handily defeated, Kuma's spirit rages on.