Sonic the Hedgehog is the main protagonist to Sonic X along with the rest of the Sonic the Hedgehog franchise. Sonic is a blue hedgehog with super speed who always fights and defeats his arch enemy, Dr. Eggman.
He made his first appearance in episode 1, when he was rescuing Cream the Rabbit and Cheese from Doctor Eggman; and during that time was transported to a whole other demension.
Sonic hails from an unnamed world in a parallel dimension to Earth. His backstory is a mystery but it's known that he befriended Tails, Knuckles, Amy, Cream and Cheese and many small animals as well as battling Eggman. One day, he attempted to rescue his friends Cream the Rabbit and Cheese the Chao from Doctor Eggman, as well as foiling the doctor's latest plot to control the world with the power of the seven Chaos Emeralds. Unfortunately, an accident initiated Chaos Control, which transported Sonic, Eggman, all of Sonic's friends, and all within a ten mile radius to Earth. On Earth, Sonic befriended Chris Thorndyke, who rescued him from drowning in a swimming pool and then allowed Sonic, Tails, Amy, Cream and Cheese to stay hidden with him in his house. He also forged a friendly rivalry with Chris' uncle, Sam Speed, a cop who chases criminals in a racecar. He is initially hidden in Chris' home and boggles the human race with his being; people think he's an alien or machine. While Sonic was mostly covert, Eggman made himself known as he tried to conquer the new world. Sonic eventually destroyed Eggman's first base and was hailed as a hero along with all of his friends. Sonic destroyed Eggman's second base by finally gathering all the Chaos Emeralds and becoming Super Sonic. After Chris dropped them into the ocean, they caused Chaos Control to bring some aspects of his world, like Angel Island, to Earth.
After the adaptations of Sonic Adventure, Sonic Adventure 2, Sonic Heroes and Sonic Battle, it was discovered that Sonic's world and Earth were merging (possibly due to Sonic bringing parts of his world to Earth) which would lead to the stopping of time. The only way to save both planets was to return Sonic and his friends home. After everyone but Sonic had went through, Chris took him away, eventually to his parents' old summer home. Chris tells Sonic how much he will miss him and how much of a friend the hedgehog was. Sonic gathers the Chaos Emeralds and, after taking Chris for one final run, returns to his home universe.
Upon returning, Super Sonic easily destroys Eggman's latest battleship, saves Tails and then meets Amy, giving her a rose and telling her that he will never leave her. (In the Japanese version, what Sonic says is muted out, and in French versions, he tells her that he loves her)
Six months later, Super Sonic battled Dark Oak in the atmosphere. He spread the Chaos Emeralds throughout space and fell back to the planet. He was found and nursed to health by Dr. Eggman. Later, the heroes gathered the Chaos Emeralds in a space journey very loosely based on Sonic Heroes and Shadow the Hedgehog. In the end, Super Sonic and Super Shadow destroyed Dark Oak and they all returned home. Sonic watched as Chris was flown away back to Earth and declared war on Eggman for making Chris leave so soon. He said, "I'll never forgive you, Eggman!" ("Life never stays slow around here for long, thank goodness! Watch out, Eggman, I'm comin' at ya full speed ahead!" in the English version). In this season, Sonic seemed to care about Amy a lot more than in seasons one and two.
Sonic is a habitual daredevil who is honest, loyal to friends, keeps his promises, and dislikes tears. He took the young Tails under his wing like a little brother. Even though he isn't intrigued by the marital proposals from Amy Rose, he really seems to share her feelings, as he even dives into water to save her when she was drowning in episode 9 (even though he couldn't swim); and in episode 52 (English version), he also promises her to never leave her alone again (in the French versions, he tells her that he loves her). In season 3, Sonic shows just how much he does care for her by putting his life on the line so that the Metarex wouldn't hurt Amy. When Sonic is dragged inside the Metarex planet, Amy tries to save him, but ends up being dragged inside the planet as well; then, a bubble suddenly appears and envelopes them both, healing and protecting them. It transports them out of the planet (it seems that something unknown had sensed how much they cared for each other and saved them when they needed it most).
With Knuckles, they have a great rivalry in their friendship. (similar to the game one). The two can be great team mates, but Sonic simply can't resist teasing him whenever he has the chance. When he met Chris at the beginning of the series, he quickly became friends with him.
In times of crisis, he focuses intensely on the challenge as if his personality had undergone an astonishing change. Sonic's greatest strength is his running speed, which is faster than the speed of sound. He appears as a blue blur when he runs. He can use the Spin Attack like in the games and appears in 3D. In this state, he can break through virtually anything and a ring can increase his power similar to SatAM.
When seven Chaos Emeralds are collected, he is able to transform into Super Sonic; a faster, stronger and invulnerable version of himself that can fly, teleport and move faster than the speed of light. He can also heal people with a touch. He has used super transformation against Perfect Chaos, Biolizard, Eggman, Dark Oak, and Super Shadow.
"Oh! What a great view!" - After running up a tree in the Japanese version of "Cracking Knuckles" in English.
"So, are you up for a race, eh?" - After he thought that the cheetah would race against him in "Dam Scam".
"Good job! Our captain!" - To comfort Tails when he thought he wasn't a good captain.
"Don't you worry Amy, I never will!" - Sonic telling Amy that he would never leave her again in episode 52.
"If I don't get to the city fast, there won't be anything left to save!" - Sonic realizing that Chaos is going on a destructive rampage.
"YOU CAN'T STOP ME!" - Sonic during his fight with the gargantuan dragon, Chaos, after the beast spat a beam of fire.
"Is that the best you can do?" - Sonic just moments before he dives into Chaos's huge jaws.
"I'd like to, but I don't get involved in fights I know I can't win. You're on your own." - When Knuckles asks Sonic for help when the girls (Amy, Cream and Cosmo; Sonic X's Team Rose) start "knocking some sense" into Knuckles in episode 54.
"Life never stays slow around here for long! Thank goodness! Watch out Eggman, I'm coming at you full speed ahead!" - In the dub version of the final episode when he declares war on Eggman.
"I'm just a guy with a need for speed! They call me "Sonic the Hedgehog"!" - Sonic while chasing Shadow on the ARK.
Sometimes, when Sonic runs, his feet move in a circular motion. This could be a reference to the 2D games as his feet would move in a similiar fashion at full speed, as well as the other three shows which appeared earlier.
Sonic also seems to have some kind of super strength; as seen when he was able to push back the E-18 Guerra-Hard robot as well as being able to hold back a fish Metarex with very little or no effort with one hand. Also, in several episodes, he's seen punching Eggman's robots.
It has been said that Sonic never cries, yet in the second season finale, episode 52, A New Start, as Sonic is carrying Chris, you can see tears coming from his face and onto Chris', as well as when he encountered Amy at her house, and when they talk (Amy actually), you can see Sonic's eyes nearly water (but only if you have a good eye) when Amy is explaining her dilema to him.
In the Japanese version, Sonic uses the most English out of all characters.
No matter what angle you see Sonic (excluding when he is falling from outer space after his first fight with Dark Oak), he has three quills. When as Super Sonic, he has five quills.
Sonic is shown to enjoy taunting Eggman by turning around, sticking out his tongue, pulling on his eye socket and slapping his rear.
Both Sonic and Chris appeared in the most episodes of Sonic X (76).
Sonic doe's not like water or is even afraid of it , he drowned in a pool in Episode 1.