Sonic Adventure is a 1998 platform game developed by Sonic Team and published by Sega for the Dreamcast. It is generally considered to be the first major 3D Platforming Sonic Game, the first entry in the Sonic Adventure Series of games, the first game in the "Modern Sonic Era", the first main series game to feature spoken dialogue/voice acting from the majority of the main cast of characters, and widely considered to be the one of the best and most important titles in the entire franchise amongst the Sonic the Hedgehog fandom. Second only to that of its sequel Sonic adventure 2.

The Plot of the game is that Dr. Eggman, formerly known as Dr. Robotnik up until this point, has come up with a new scheme to take over the world by awakening and enlisting the power of and ancient being known as Chaos. Chaos, who has the ability to permanently integrate the Chaos Emeralds and their power into its body and evolve in turn, proves to be an incredibly formidable enemy for Sonic the Hedgehog and his friends.

The game notably features the option to play as six different characters with their own unique abilities, playstyles, campaigns, and versions of the story throughout. You can play as Sonic the Hedgehog, Miles Prower, Knuckles the Echidna, Amy Rose, Big the Cat, and E-102 Gamma.

The game also notably includes the introduction of the Chao and the Chao Garden, the knuckles tribe, Tikal the Echidna, and the larger lore of the series.