Roysten

Roysten is Banjo's pet goldfish. He appears in all of the games but is mostly a background character (except in Banjo-Tooie) serving little purpose aside from showing up in humerous/dangerous situations.

Banjo-Kazooie
He appears on a shelf in Banjo's House swimming around then tapping the glass of his bowl. Near the end of the game Mumbo Jumbo is seen grilling Roysten on a barbeque.

Banjo-Tooie
In Banjo-Tooie, he is knocked off the barbeque when Gruntilda blows up Banjo's house and becomes trapped under a boulder that must be smashed using the Bill Drill ability. Once Roysten has been rescued and released into the moat around Spiral Mountain, he teaches Banjo and Kazooie how to swim faster and doubles their air capacity.

Banjo-Kazooie: Grunty's Revenge
Roysten makes a cameo appearence in Grunty's Revenge, still stuck on the barbeque from Banjo-Kazooie (this game takes place between Banjo-Kazooie and Banjo-Tooie)

Banjo-Pilot
Roysten appears in the background of the trophy room inside his fishbowl.

Other Games
Roysten appears as a character in Grabbed by the Ghoulies.