Big the Cat first debuted in Sonic Adventure where he was introduced as a fisherman living in the Mystic Ruins. Big's existence is shown to be disconnected from the more civilised world but he does carry a strong affinity for his non-anthropomorphic frog companion Froggy who he has kept up a long-running friendship with. Big is also the bearer of one of the seven Chaos Emeralds, although he appears to be oblivious to the importance or power of the emerald as he refers to it as his "Lucky charm".
Unknown to Big, the malevolent being Chaos possesses Froggy and makes him eat Big's Chaos Emerald before hopping away. Big then follows Froggy through the game, with the player participating in a fishing minigame in each of his levels. Big eventually finds himself on Eggman's attack ship after Eggman's robot E-102 Gamma picks up Froggy. Big is later there when Froggy is absorbed by the larger Chaos being for the use of his Emerald, but he is reunited with Froggy after Sonic defeats Chaos. At the end of his story, Big is shown to return to the Mystic Ruins to frolic there with his companion.
Big later plays a key part in Sonic Heroes, acting as the "Power" character alongside Amy Rose and Cream the Rabbit in "Team Rose". His abilities include a belly flop which damages enemies beneath him, being able to float through the air via parasol, and using that same parasol to hit enemies. During the game he once again searches for Froggy who he eventually recovers from a defeated Eggman robot.
Outside of these appearances Big has few other major playable roles and is largely relegated to cameo appearances, slots in sports-based spin-off games, and handheld titles. Sega eventually began to phase the character out of the games in the early-mid 2010s.