Here's a list of characters in the Sonic the Hedgehog games in alphabetical order:
Amy Rose
Babylon Rogues
Big the Cat
Blaze the Cat
Chao
Chaos
Chaotix
Cream the Rabbit
Doctor Eggman (Robotnik)
E-100 Series
Fang the Sniper
Gizoids
Guardian Units of Nations
Knuckles the Echidna
Maria Robotnik
Metal Sonic
Miles "Tails" Prower
Omochao
President
Professor Gerald Robotnik
Rouge the Bat
Shadow the Hedgehog
Silver the Hedgehog
Sonic the Hedgehog
Tikal the Echidna
The first characters are Sonic the Hedgehog and Doctor Robotnic (later called Dr Egghead), from the very first game, in which Robotnik had trapped animals from the forest in his robot henchmen.
The next character to join the series is Miles "Tails" Prower, in Sonic the Hedgehog 2, in which a second player could control Tails. Metal Sonic also makes his/it's first appearance.
After that Knuckles the Echidna joined in Sonic the Hedgehog 3. He is the protector of Angel Island and the Master Emerald kept there, and he sets off a trap to prevent Sonic's advance in the forest. Eventually he becoms an ally to Sonic.
Some new characters are introduced in Knuckle's Chaotix.
A bunch of new characters appeared in Sonic Adventure on the Dreamcast.
Among them, Chaos is the first one you see ( in the opening sequence). You also meet omochao and the chaos ( not to be confused with Chaos :P) for the first time.
Some new playable characters are available, Big the Cat ( along with him Froggy), Amy Rose and the E-102 Gamma robot. You also meet Tikal the Echidna, a spiritual help to Knuckles.
In Sonic Adventure 2 once again new characters are introduced.
Sonic's rival Shadow the Hedgehog is a biological experiment to produce the ultimate lifeform. He is confused for Sonic in the beginning of the game. His only friend while in the research facility was Maria Robotnik, who rescued him and motivated him to fight for man kind. He was created by Professor Gerald Robotnik in an attempt to cure his granddaughter Maria.
Rouge the Bat is a new playable character who at first glance seems to join Dr. Eggman just for a chance to steal some valuable jewels. She is however working as an undercover agent for the president.
There are some new chaos, like the doctor, psychic, teacher and merchant in the black market. These aren't recurring characters though.
Chat with our AI personalities
All the Sonic characters are single, aside from Amy as she likes Sonic and Sonic because Amy will most likely kill the girl if he ever got a girlfriend.
Not All the Characters but a Few...
go to the address below when you get on the page, scroll half way down and you should see SONIC BATTLE M.E with all the sonic characters appearing . its a full mugen game, but if you just want the characters then open the folder named "CHARS" . all the sonic characters will be there. http://mugencharacters.ucoz.com/
June 23rd
All the characters in Sonic All Stars Transformed are unlocked by completing all levels of the game. Some characters require certain goals like race points but most of these are automatically achieved upon completing the game.