Prior to his capture, Bosco lived in the forests along the eastern coast of the Earth Kingdom. He was the only known member of his species, although the Earth King had commanded the top zoologists of Ba Sing Se University to lead a battalion of soldiers in scouring the Earth to find Bosco a mate. Little is known about his habits in the wild; however, Bosco enjoyed roaming the grounds of the Royal Palace with his master, and he developed a taste for cakes and pies, hence his weight.
Bosco was the guest of honor at a birthday party the Earth King threw for him, where he ate large portions of food and was fascinated when Aang performed waterbending tricks.
He frequently sat at Kuei's side and was one of the prime reasons Kuei decided to hear what Aang and his friends had to say about the conspiracy in Ba Sing Se, as Bosco took a liking to Aang.
Bosco was at Kuei's side when he welcomed the disguised trio of Azula, Mai, and Ty Lee. Apparently, Mai was forced to clean all of Bosco's waste, stating that "if [she had to] clean another pile of bear poop, [she would] throw up." Bosco was separated from Kuei after Azula ordered the Dai Li to arrest the King, but was soon reunited with his master when Sokka and Toph rescued him from Ty Lee and Mai.
After the Coup of Ba Sing Se, Sokka tried to teach Bosco to survive in the wild, though he gave up after many failed attempts of teaching him how to climb, fish, roar, and defend himself. Subsequently, Bosco was the main reason for Kuei's decision to roam the Earth Kingdom as he realized that just as Bosco had limited knowledge of being a bear, he too had limited knowledge of being a king. Thus, both left Team Avatar to travel the world undercover.
Following the liberation of Ba Sing Se and the end of the Hundred Year War, Bosco returned to a life of luxury once more when Kuei regained his position as Earth King. During the planning of the Harmony Restoration Movement, Bosco was present in the throne room with Team Avatar and the Earth King. While they discussed the plan, Momo tried to steal Bosco's hat, though the bear quickly snatched it back. Bosco was present a while later at the richly-filled dinner table the King had prepared for Aang and Katara to occupy them while he was pondering the changed situation in Yu Dao. During this, Momo offered him a small piece of cake on a plate, but Bosco turned his head away in refusal. The bear subsequently tried to reciprocate the gesture with a fish, but the lemur rejected it earnestly.
After Kuei's death, Bosco was eaten by Earth Queen Hou-Ting. Afterward, rumors about his demise spread in the Earth Kingdom.
Bosco was ill-mannered, loud, and spent a great deal of time eating. However, the Earth King apparently was oblivious to his pet's faults and treated the bear like a son, taking Bosco along to see the world incognito outside the walls of Ba Sing Se after the city fell. Despite his less genteel qualities, Bosco was affectionate toward Kuei and others and could sense if danger was near or if someone was a good person. He was also highly intelligent, not only able to perform human activities, like using a fishing rod, but also to fully understand human language. Bosco was also playful and energetic, especially when around friendly human companions. As a talented whistler, Bosco preferred not to roar.
When Bosco was first mentioned to Aang and his friends, they were skeptical that there was such a creature as "just a bear" and suggested that perhaps it was another type of creature, such as a platypus bear, skunk bear, armadillo bear, or gopher bear.