Banjo's first event of any significance in his life is when he first met Kazooie. Banjo made his home in Spiral Mountain with Kazooie and his sister Tooty. He was content to live in his small neck of the woods, but the other two bugged him to go on an adventure sometime.
In 1997, just before Banjo was convinced to have an adventure, he got a message delivered by Squawks the Parrot from Diddy Kong, asking for help in driving Wizpig off Timber's Island. Banjo gladly helped, but didn't think that racing really agreed with him.
A year later, Banjo finally caved in and planned an adventure with Kazooie and Tooty. The day they were to go on an adventure, Tooty was kidnapped by Gruntilda for her beauty, leading to a rescue operation. Normally Banjo wouldn't bravely storm into a witch's lair full of bear-smiting traps, but the capture of Tooty and the prodding of Kazooie lead him to go. Using teamwork and a series of moves taught by Bottles, Banjo saved his sister and buried the witch.
However, two months later the witch's minion Klungo transplanted Grunty's spirit into a time-altering suit. Gruntilda proceeded to capture Kazooie and mess up time, preventing the duo from meeting in the first place. But with the help of some Mumbo magic, Banjo was able to give chase, rescue his friend and beat down Grunty a second time.
In the peaceful period that followed, Banjo mostly enjoyed life. However, two years later the witch returned in Banjo-Tooie when she was set free by her sisters and she destroyed Banjo's house, killing Bottles. Banjo sets out with Kazooie once more to stop the witch and her two sisters from zapping the whole island of its life-force to give Gruntilda a new body and hopefully finding a way of reviving Bottles as well as the now undead Jinjo king. Using Bottles' brother Jamjars as a teacher, Banjo learned how to operate with an empty backpack and use Kazooie as a handgun - which was the definitive moment in stopping Grunty for the third time.
With no witch to worry about any more, Banjo started to fix up his house (but gave up halfway through) and live the carefree life. He ate pizza all day and slept all night, leading to him becoming temporarily obese.
After a while, in 2008, Grunty came back again. But this time, she was followed by a mysterious being called L.O.G., who devised a competition to see who will own Spiral Mountain. With his quadruple-chins and obesity magically removed, Banjo was anxious to earn the rights to his home and got to work. After a long test of vehicular combat, he won the challenge and Spiral Mountain's deeds.
Then in 2010, Banjo got word of a racing tournament of some sort. He decided to put his old racing skills to the test, so he and Kazooie fixed up the 'Bolt Bucket' and went out racing with Sonic and friends.
According to Banjo-Kazooie: Grunty's Revenge, Kazooie was originally discovered by Banjo on Breegull Beach inside the blue backpack one day. For whatever reason, the two became friends at some point after that and Kazooie lived an annoyingly-quiet life with Banjo and his sister Tooty for an unknown period of time.
In 1998, Kazooie finally convinced Banjo to go out on an adventure somewhere, although Banjo insisted on taking Tooty along as well. Kazooie got her wish when Gruntilda captured Tooty, forcing a rescue operation. Kazooie thoroughly enjoyed learning cool moves and witch-bashing, although having to deal with Bottles, Mumbo Jumbo and Banjo's constant desire to help everyone was a constant pain in the butt to her. Eventually, Grunty was buried and Tooty saved.
A few months afterward, Klungo devised a plan for Grunty to escape her rock prison and go back in time, preventing Banjo and Kazooie from ever meeting. Kazooie was taken back in time by Mecha-Grunty in order to prevent her past self from meeting up with Banjo. Luckily, Banjo followed Grunty and, with help from Mumbo and Bottles' ancestor, rescued Kazooie. The two of them proceeded to beat Grunty and restore the timeline.
Convinced that they had not seen the last of Gruntilda, Kazooie insisted that she and Banjo continue practicing their moves and refining their abilities. In 2000, her instincts proved correct when Gruntilda's sisters Mingella and Blobbelda rescued her and destroyed Banjo's House in the process, killing Bottles. Kazooie was instantly pumped to get off on another adventure and, while Bottles' brother Jamjars was every bit as annoying to her as Bottles himself was, she learned to separate from Banjo and lay the hurt on the witch's minions herself. After defeating Grunty a second time and reviving everyone who died, the duo went into "rest mode" once more.
Kazooie, however, wasn't pleased with sitting around and doing nothing. She jabbered constantly at Banjo to keep practicing moves. Banjo flatly refused this time, deciding instead to start fixing up his house for a few weeks. After that, the pair slipped into a depressing lifestyle of boredom, Xbox 360 and pizza.
After eight whole years of nothing, Grunty reappeared in 2008. However, another being also revealed himself: The Lord of Games, a near-omnipotent character that set up a vehicle-based challenge between Banjo and Kazooie and Gruntilda for the rights to Spiral Mountain. Kazooie was not one bit happy about this, since L.O.G. had swapped her moves for a magical wrench. After an arduous journey in which Kazooie constantly felt as if she got the shaft, Banjo finally defeated Grunty and legally earned the deeds to his home. Kazooie also got her old moves back, so the adventure wasn't a total waste after all.
Then in 2010, Kazooie heard rumors of a racing tournament starring a blue hedgehog of some sort. Kazooie helped Banjo fix up the 'Bolt Bucket' and join in the race against Sonic and friends.
Banjo's personality is very different from that of Kazooie's. Banjo is a well-mannered, sweet-natured, easygoing bear. He uses "Mr." or "Mrs." when speaking to people and generally likes to help people out - which means a lot of damage control when Kazooie opens her beak. While he always means well, he sometimes comes off as a bit slow. He tries to say something witty every now and again, but he usually isn't any good at it. Banjo flip-flops a bit when it comes to his bravery - at times he will jump into a situation quickly, but other times he acts timid and doesn't want to commit. In all cases, however, he would much rather sit down and have either honey, pizza or a nap, suggesting he is somewhat lazy. Throughout the series (mostly in Nuts & Bolts), many characters including Banjo's allies have referred to Banjo as "stupid" and "crazy", but this is a trait not shown in other games in the series.
Banjo's relationship with his younger sister Tooty probably hints that he cares for her deep down inside, since he did ask about her whereabouts when she was captured and even accepted the fact that of all the prizes won at the Furnace Fun in Banjo-Kazooie, it was her he was thinking on taking along. Banjo doesn't at all seem to mind Tooty's company at times since he saw no problem when she began her flute solo in the opening.
Kazooie's personality is very different from Banjo's. She is a wisecracking, sassy, cheeky, hot-tempered, slightly egotistic, tell-it-like-it-is loudmouth. This could be because almost everyone that Kazooie has met had insulted her in some way. Bottles, for example, called her a 'strange friend' and asked Banjo if she could talk and Mumbo Jumbo called her the 'filthy feathered one'. This could also be why Banjo and Kazooie are such great friends since Banjo hardly ever insults anyone (and if he does he usually apologizes).
Kazooie likes adventuring (something which Banjo hates) and saving the world while she hates boredom, Banjo's lack of an attitude and facing backwards. During screensaver mode in Banjo-Kazooie and Banjo-Tooie, Kazooie will suddenly poke her head out the backpack and peck at Banjo's head for the fun of it. In Banjo Tooie, half the time Banjo might get irritated by this and wring her by the neck, choking her momentarily without doing any damage. Obviously, this may resolve that Kazooie is a bit of a prankster.
Despite Kazooie's foulmouthed rudeness, she never insults Banjo at all. Being best friends and both with different personalities, it's obvious that she respects him greatly and will stop insulting upon Banjo's words, proving her loyalty to him. Despite all her flaws, Kazooie still has a good heart, always willing to help those in need (Provided that it has something to do with the adventure) and she has a strong sense of justice. She hates evil, like Gruntilda, and takes pleasure in defeating enemies.
Banjo cannot run very fast and his jumping often requires some bird-enabled help. When Kazooie leaves the safety of his backpack, Banjo can use it in a variety of ways, such as an impromptu sleeping bag or a potato sack, not to mention as his sole offensive weapon. The backpack also seems to have an infinite storage capacity, containing most items with ease. Banjo, being a bear, is an excellent swimmer and has learned how to paddle faster and hold his breath longer. Unlike Kazooie, Banjo has the ability to climb structures and grasp ledges with his fingers, allowing access to difficult to reach spots on the duo's adventures.
When Banjo is paired with Kazooie, he has a lot more skills at his disposal. The duo can perform a Forward Roll while running to attack enemies; Kazooie can use Banjo as leverage to perform the Rat-a-tat Rap; they can fly through the use of flight pads and utilize Kazooie's ability to fire different types of eggs.
Banjo also has access to the powerful magical abilities of his allies Mumbo Jumbo and Humba Wumba. Depending on the game, one of the two will grant Banjo and Kazooie the ability to transform into different creatures, each with its own unique skills and powers.
In Banjo-Kazooie: Nuts and Bolts, the Bear and Bird have forgotten their abilities and instead must battle their arch-nemesis Gruntilda the Witch by creating awe-inspiring vehicles for all sorts of terrain and conditions. With an almost unlimited assortment of weaponry and gadgets to add to these machines, Banjo and Kazooie will no doubt be ready for whatever challenges their new adventures may bring. Kazooie is also given a magical wrench used to smack enemies as well as magically carry objects and turn pipes. She attacks with it from the safety of Banjo's backpack.
In Sonic & Sega All-Stars Racing with Banjo-Kazooie, Kazooie pecks Banjo on the back of the head and then drops Jiggies on their opponents with her magical wrench.
Aside from fitting into a backpack with no apparent discomfort, Kazooie can fly, climb steep slopes that Banjo cannot, shoot eggs out of her beak and backside, become invulnerable for a limited time, attack enemies with her wings and hatch large eggs when alone. In Banjo-Tooie, if the Mega Glowbo is given to Humba Wumba, Kazooie is able to transform into the ferocious Dragon Kazooie.
When paired with Banjo, Kazooie has even more skills at her disposal. The duo can perform a Forward Roll while running to attack enemies. Kazooie can use Banjo as leverage to perform a fast Peck attack. She can also enjoy Banjo's excellent swimming abilities and his ability to climb and grasp ledges, among other useful skills.
In Banjo-Kazooie: Nuts and Bolts, the Bird and Bear have forgotten their abilities and instead must battle their arch-nemesis Gruntilda the Witch by creating awe-inspiring vehicles for all sorts of terrain and conditions. With an almost unlimited assortment of weaponry and gadgets to add to these machines, Banjo and Kazooie will no doubt be ready for whatever challenges their new adventures may bring. Kazooie is also given a magical wrench that not only allows her to smack her enemies, but also lets her magically carry objects and turn pipes. She attacks with it from the safety of Banjo's backpack.
When getting the All-Star-Move in Sonic & Sega All-Stars Racing with Banjo-Kazooie, Kazooie swings the magical wrench she got in Banjo-Kazooie: Nuts and Bolts in the air to call up a "Jiggy rain". While doing that the typical Banjo-Kazooie music is playing.