Awesome Backpack: His trademark blue backpack, used to carry Kazooie. He can use it as a weapon and as a healing item in Tooie.
Aww, Look! They Really Do Love Each Other: Despite their griping, when he and Kazooie are separated in Tooie and go in radically different directions, the left-behind character will tell the other to come back for them. Also, in Grunty's Revenge, when Kazooie picks up the Distress Ball, and Banjo reunites with her, the two are happy to see each other again!
Beary Friendly: Will try and make pleasant conversation to you even if you're a boss character who's about to try and murder him. His friendliness is even more apparent since he's always with Kazooie.
Big Brother Instinct: For what little interaction we see between Banjo and his sister, he is protective of her.
Brilliant but Lazy: He's determined to save his sister no matter the hazards awaiting on their journey, but when he isn't doing some heroic rescuing, he'd rather slack around and play video games.
Funetik Aksent: Has an exaggerated southern voice, judging from his sole line of dialogue in Diddy Kong Racing. His normal in-game grunts are more falsetto-esque.
Genius Ditz: He manages to win at Gruntilda's trivia games in both Kazooie and Tooie despite his aforementioned simple-mindedness.
Kindhearted Simpleton: Much more affable and friendly than Kazooie. Worth noting, though, that as of Nuts and Bolts, he seems to have picked up on some of her cynicism.
Mighty Glacier: Unlike Kazooie, he loses very few of the team's combined honeycomb max when split up. He also can't move very quickly without Kazooie. Pack Whack, his basic attack, even does twice as much damage as Wing Whack.
Not a Morning Person: Because of this, he sleeps right through the racket that was his sister being kidnapped.
Only Sane Bear: In a world with giant cyborg sharks and sentient, visually impaired welding torches, he will make the utmost effort(?) to not notice and carry on as normal.
Action Girl: Banjo can only do four things without Kazooie's help: punch, jump, run and roll. In Tooie the punch is replaced by Kazooie's beak attacks and she even helps with the rolling. She also runs faster than Banjo and extends his jumps.
Deadpan Snarker: Oh, you say you're some amazing animal/giant creature/inanimate object that wants to fight and/or have an errand that needs doing? Not without your motives and the unlikeliness of your situation being questioned first. She's also known for dismissing a boss' Bad Ass Boast with a dismissive, "That's Nice".
Distress Ball: Picks this up at the beginning of Grunty's Revenge. Justified due to the fact that Gruntilda was using time travel.
Good with Numbers: At one point, when confronted with a four-digit safe in Tooie that supposedly has an unlimited number of combinations, she offers up that it's only able to give 10,000 possible combinations.
Green Eyes: Signifying her "spitfire" personality.
Hypercompetent Sidekick: Note that Banjo's not incompetent, but Kazooie is responsible for the majority of the moves the two share. As such, she also maintains most of the learned moves when the two split up, while Banjo has to learn moves before he can do anything but run and jump. (It should be noted that going by the first game, Banjo should have an A attack. This move was removed and replaced with one relying on Kazooie.)
Tsundere: Speaking to a lost baby alien in Tooie reveals her soft side. In fact, Kazooie is an interesting THIRD type of Tsundere: she manages to be both caustic and sentimental at the same time, always.
Vitriolic Best Buds: With Banjo. Their constant bickering coupled with weird tolerance for each other's differences could only mean this.
Mumbo Jumbo the Shaman
The former mentor of Gruntilda the Witch until he turned his back on her, prompting her to magically trap Mumbo's face inside of a wooden mask. In the first game, he helps out Banjo and Kazooie by providing transformation spells in exchange for Mumbo Tokens. In Tooie, he takes a more active role, allowing you to play as him and use spells in certain locations. In Nuts and Bolts, he's taken up a job as a garage mechanic.
Body Horror: Grunty's spell on his face, which apparently never wore off after she was beaten. In Nuts and Bolts, it's gotten to the point where it's even become his actual face—and he can even pull out his eyes and juggle them!
Heel-Face Turn: Was a mentor to Grunty until she turned his face into a skull.
Squishy Wizard: Actually kind of averted. He's not that squishy (only one honeycomb less than Banjo-Kazooie together), but the main reason that you play as Mumbo in Tooie is so you can make use of his various magic spells.
Static Stun Gun: Staff actually, and it's able to kill enemies too. It's Mumbo's only attack when he's playable in Tooie.
The mentor of Banjo and Kazooie in the first game. Throughout the game, he pops up via molehills, providing new abilities to help them beat Gruntilda. In the opening of the second game, he is killed by Gruntilda when she destroys Banjo's house, prompting Banjo to get revenge on Grunty—although he is revived in the end of the game. He has a minor role in Nuts and Bolts.
Spanner in the Works: Implied in The Stinger for Banjo-Kazooie: Nuts And Bolts, where she mentioned that being sent to work at the video game factory due to losing the deed for Spiral Mountain was a big mistake, as now she has the resources to create her own game.
Banjo's younger sister, who was kidnapped by Gruntilda in the first game due to her being "the fairest in the land", so that Grunty could swap her ugliness for Tooty's beauty. Despite being the entire reason the enmity between Banjo and Gruntilda even began, she doesn't make any appearances outside the original game, save for a cameo in Tooie where she's seen on a milk carton.
Came Back Wrong: In the alternate ending of the first game, where she is turned into a large, hideous monster after having her beauty sucked out and Grunty's ugliness put into her.
Chuck Cunningham Syndrome: Enough to even get a lampshade from Rare, explaining that her reason for not appearing in Nuts and Bolts was because she was hauled off by the "Rubbish Video Game Characters Police".
Her absence was also lampshaded in Tooie where her face is seen on a milk carton.
The Igor-esque right hand monster of Grunty in the first game. He had a minor role in the first game, but was presented as a loyal, competent sidekick to Grunty. This gets thrown right out the window in Tooie, making him a minor boss character who gets physically worse and worse as you meet him in the game, due to his beatings from Grunty. Afterwards, he left to become a video game designer.
A camel found in the titular Gobi's Valley. Banjo and Kazooie find him chained to a rock and free him, earning them a Jiggy, and meet him several times afterwards; each time ends with the poor camel getting slammed on the back and losing some of his water.
Butt Monkey: Every time the duo meets him, they Beak Bust his back to use some of his water, much to his annoyance. His attempt at leaving where they would never find him only got him captured again. And even after they save him, they have to use his water one last time anyway.
Distressed Dude: Twice. Once in Gobi's Valley, then in Witchyworld in Tooie.
Foreshadowing: When you whack him for the final time in the first game, he leaves for the lava world, where Banjo and Kazooie would never find him. Come Banjo-Tooie, and true to his words, he heads to the lava side of Hailfire Peaks as soon as you free him.note It should be mentioned that the latter level was going to be in the first game as Mount Fire Eyes, so maybe Gobi was referring to that. However, since Mount Fire Eyes was cut due to time constraints and later readapted into the fire side of Hailfire Peaks, it works as a foreshadowing anyway.