*The following descriptions only apply to Sonic RPG.
Sonic the Hedgehog
Sonic is a blue, wise-cracking, anthropomorphic hedgehog from the planet of Mobius and is the main protagonist of the Sonic RPG series. Sonic is capable of running at supersonic speeds and is able to transform into Super Sonic. In this yellow form, Sonic's speed and strength is greatly increased, he is able to fly and he can shoot energy blasts. Originally requiring the 7 Chaos Emeralds to transform into his Super Form, Sonic is now able to transform simply at will with the right amount of energy. This is due to an accident with the Master Emerald.
Shadow the Hedgehog
Shadow the Hedgehog is a black, anthropomorphic hedgehog and an anti-hero from Mobius who is very independent, determined and arrogant. He was created as the "Ultimate Lifeform" by Dr. Gerald Robotnik through genetic experimentation. Shadow has fought both for and against Sonic and his friends in the past. His hover shoes enable him to propel himself at extreme speeds that rival that of Sonic. He is also able to use Chaos Emeralds to manipulate time and space through a move called "Chaos Control." Shadow was initially the strongest of all player characters, until Dr. Eggman stole his Chaos Emerald, forcing him to join Sonic and the others for support.
Knuckles the Echidna
Knuckles is a red, anthropomorphic echidna who is physically strong an resilient. He has a short temper and often acts on impulse. He is the last guardian of the Master Emerald and one of Sonic's friends.
NiGHTS is a Nightmaren of Herbegitan, a land in another dimension. He is noble and hospitable, and he possesses numerous magical abilities. He was once the emperor of the Light Half of Herbegitan, until his older brother Reala, emperor of the Dark Half, allied himself with Seelkadoom and conquered all of Herbegitan. In order to restore the balance of the land, NiGHTS is allied with Sonic and the other heroes from Mobius.
Miles "Tails" Prower
Tails is a yellow, anthropomorphic fox. He is known as Sonic's sidekick and best friend. He is able to use his two tails to propel himself into the air like a helicopter. He is also an expert mechanic. Since he is less physically capable compared to his teammates, he often uses his fighting machines in combat. While Sonic is lost in another dimension, it is Tails' duty to defend Mobius against Dr. Eggman's evil plans.
Seelkadoom the Hedgehog
Seelkadoom is the main and most powerful antagonist of the series. He was created by Dr. Eggman, grandson of Dr. Gerald Robotnik, through the combination of Sonic and Shadow's DNA and battle data, and the manipulation of Chaos energy. He is Dr. Eggman's continuation of his grandfather's work in genetic experimentation; revival the long-terminated project was a grave mistake. Immediately after his birth, Seelkadoom turned on his own creator and became as massively power-hungry enemy of all.
Reala is a nightmaren from Herbegitan. He is NiGHTS' older, cruel, insidious brother and the emperor of the Dark Half of Herbegitan. He possesses similar skills to his brother. When Seelkadoom arrives at Herbegitan, he allies himself with Reala and takes command of his empire, Reala too afraid of Seelkadoom's power to object.
Dr. Ivo "Eggman" Robotnik
Dr. Eggman is the grandson of Dr. Gerald Robotnik. He is constantly attempting to build his Egg Empire, unleashing many plots, all of which are ruined by Sonic and his friends. Dr. Eggman has created many robots, machines and genetic experiments to do his bidding. One of his most recent plans for building his empire was to create genetically modified lifeforms, similar to his grandfather's creation, Shadow the Hedgehog. When his prototype Seelkadoom betrays him, Dr. Eggman sends him to another dimension with his portal-opening device, along with Sonic, Shadow and Knuckles.