Big the Cat is a large, 18-year-old, purple anthropomorphic cat with yellow eyes and long ears who first debuted in Sonic Adventure on the Dreamcast. Big is laid-back and easygoing, which is reflected in his speech. Strong but gentle and a little slow, he also appears as a playable Character sonic and sega all-star racing accessdate 2010 he lives a normally peaceful life in the jungle with his best friend "Froggy". He loves fishing, and he is never without his favorite rod and lure.

He has appeared in various games as one of the main playable characters, or by making cameos. He first appeared in Sonic Adventure, where he is after his best friend, Froggy, who swallows a Chaos Emerald, and Chaos' tail. With the help of Sonic he stops Chaos and saves Froggy, later helping Sonic defeat him permanently by giving him one of the Chaos Emeralds. Next, he appeared in Sonic Heroes helping Team Rose save Froggy and Chocola (Cheese's twin brother) who had been kidnapped by Metal Sonic, gain Chaos' data, and help stop Metal Madness. He appeared in Sonic Chronicles: The Dark Brotherhood as one of the main characters in the story mode. He is found in Mystic Ruins and is the fifth character to join the team. Big is also vital for many areas in that game. His next appearance will be in Sonic & Sega All-Stars Racing as one of the playable characters. He rides a small green motorcycle and his All-Star move is to have his buddy Froggy grow huge. Then, Big grabs on to his tail and Froggy rams into Big's opponents.

He made cameo appearances in Sonic Adventure 2, Sonic and the Secret Rings, and Mario & Sonic at the Olympic Games as one of the referees. He has also appeared in the animated series Sonic X, where he made his debut on the Sonic Adventure story arc, and in the Sonic X comic. He has been voiced by the late Shun Yashiro and Takashi Nagasako in Japanese, and Jon St. John and Pete Zarustica in English.

Big was featured in a McDonald's promotion between December 3 and December 27, 2004. One of eight handheld dedicated consoles packaged with Happy Meals featured Big recreationally fishing.

Xbox World's preview of Sonic Heroes called Big the "gay best friend" of Amy and Cream.[18] In a preview of Sonic and the Secret Rings, Nintendo Power praised the exclusion of Big from the game, referring to him as a "dim-witted, morbidly obese feline". However, Big later made his way into the game.