Short answers, pulled from the story.
Chocobos are a fictional species of galliform bird created for the Final Fantasy franchise by Square Enix, originally Square. They typically have yellow feathers and have appeared in nearly every Final Fantasy title, primarily as a means of transportation across the world map.
Koichi Ishii, an artist and game designer who worked on the original Final Fantasy (1987) and Final Fantasy II (1988), created the Chocobo. The design was inspired by the memory of a pet chick Ishii bought at a festival market as a child and later lost when his parents gave it away; the Chocobo's body shape was modeled on the chick's middle stage before it matured into a chicken.
The Chocobo first appeared in Final Fantasy II, released in 1988, in the limited role of a temporary mount. Ishii had intended a more substantial companion role, which he later realized in Final Fantasy Adventure (1991), the first project where he had creative control.
The Chocobo is known for its distinctive "Kweh" call. The name "Chocobo" was inspired by the Chocoball, a popular Japanese confection made by Morinaga & Company.
The Chocobo subseries spans nearly twenty entries across game consoles and mobile platforms in multiple genres. It began in 1997 with Chocobo no Fushigi na Dungeon, a spin-off connected to the Mystery Dungeon franchise, though relatively few entries have been released outside Japan.
Nobuo Uematsu composed the original Chocobo theme for Final Fantasy II. He remixed or redid the theme for subsequent entries, applying a personal rule that each genre he selected for a remix had to share the same number of syllables as the word "chocobo".