Sonic[edit]
Sonic, the main protagonist (as usual). When Sonic and "Tails" trashed Dr. "Eggman's" Death Egg back in the events of Sonic the Hedgehog 2, they found out that spaceship wasn't destroyed, but instead crash landed on the Floating Island. When Sonic and his buddy headed to the Island, they were ambushed by Knuckles the Echidna. Knuckles steals all of Sonic and Tails' collected Chaos Emeralds. Sonic then begins his chase after Knuckles, the Chaos Emeralds, and the Doctor, beginning his storyline in the game.
Sonic hasn't changed much from Sonic 2. He's gotten a new Spin Attack move though, called the Double Spin Attack which extends the radius of his normal Spin Attack. He's also got a few other moves he can perform when he's wearing different barriers. With the Magnetic Barrier, he can perform a double jump. With the Heat Barrier, he can perform a Fireball Spin Dash, and with the Water Barrier, he can perform a Bounce Attack. Super Sonic can still be achieved with the help of seven Chaos Emeralds and 50 Rings, but there's also a hidden item in the game called an "S" Item Box that instantly grants any character 50 Rings and Super Transformation. When locked onto Sonic & Knuckles, by collecting the Super Emeralds, Sonic can become Hyper Sonic. (See that guide for more information.)
Miles "Tails" Prower[edit]
Miles' role in the story isn't much different from Sonic's. His basic gameplay is similar to Sonic's as well. Miles, however, can fly and swim, in exchange for not being able to perform any special shield attacks. Unlike Sonic, Miles can only transform into "Super Miles" using the Super Emeralds (when locked onto Sonic & Knuckles) or hitting an "S" item box. He can only transform with the Chaos Emeralds alone in a prototype version of the game. Even without a Super Form though, Tails has an overall easier game than Sonic thanks to his flight-type abilities. He is recommended for beginners.
Dr. "Eggman" Robotnik[edit]
Dr. Robotnik is at it again! After his defeat in Sonic 2, Dr. Robotnik's Death Egg crash landed on Floating Island. After wandering around the Island for a bit, he meets an echidna named Knuckles, who is native to the island. He managed to trick Knuckles into thinking Sonic and Miles were on the Island attempting to steal the Master Emerald, the object that keeps the Floating Island floating. But what could the Master Emerald have to do with Robotnik's latest plot? This and more are revealed in the second part of the game.