Sonic...

A world divided into two worlds (The current official version)
In the main games, Sonic's world is actually planet Earth, but with one peculiarity: it is divided into two types of zones:
Human zones: Modern and technological cities similar to our own (like Station Square or Central City), where humans and the President live.
Anthropomorphic Zones: Islands and fantasy landscapes where Sonic and his animal friends live. They are places full of nature, ancient ruins, and, interestingly, lots of loops, ramps, and speed boosts floating in the air!
2. Iconic places in their universe
Sonic doesn't usually live in one permanent home (he's a vagabond who loves to travel), but these are the most important places in his world:
South Island: This is where it all began. A beautiful island that constantly moves across the ocean due to the power of the Chaos Emeralds. Here you'll find the famous Green Hill Zone, with its green hills and checkered floors.
Christmas Island: According to the official manuals, it is Sonic's birthplace.
Angel Island: A huge floating island that stays in the sky thanks to the Master Emerald, which is protected by Knuckles.
3. Magical elements of their world
The Sonic universe is filled with a very powerful mystical energy:
The Chaos Emeralds: These are seven mystical gems of infinite power that grant wishes, transform Sonic into Super Sonic, and can alter space-time (the famous Chaos Control).
The Rings (Golden Rings): They are scattered throughout his world. They grant him energy and protect him from attacks.

A lover of freedom: He doesn't like being told what to do or being confined. He lives by his own rules and travels the world seeking new adventures. His motto is to live life to the fullest.
Confident and a little boastful: He knows perfectly well how fast and talented he is, so sometimes he can be a little conceited or mocking, especially with his enemies (like Dr. Eggman).
Impatient: Because he runs at the speed of sound, the real world sometimes seems too slow to him. He hates being still and gets bored extremely easily if there's no action.
Loyal and protective: Although he may seem like a lone wolf, he would give his life for his friends (like Tails, Knuckles, or Amy). He can't stand to see others suffer and is always willing to help the helpless.
Unwavering sense of justice: He doesn't seek to be a hero for fame or recognition; he simply does what is right because it is what his heart dictates. He has a very strong code of honor.
Relaxed but determined: In the face of danger, you'll rarely see him scared or lose his composure. He usually takes threats with humor and a smile, but when the situation gets really serious, he focuses completely on winning.

Species and color: It is an anthropomorphic hedgehog with a bright blue color on most of its body.
Skin: Its face (around the eyes and snout), the inside of its ears, and its arms are a peach or light flesh color. It also has a circle of this same color on its chest/belly.
Spikes: It has six large spikes on the back of its head that point backwards, and two spikes on its back.
Eyes: In its modern version, it has large, emerald-green eyes. (In the classic 90s games, its eyes were completely black.) Its eyes are connected in the center of its face.
Clothing and accessories:
He wears white gloves on his hands.
She wears very striking red sneakers, which have a gold buckle on the sides and a horizontal white stripe in the center.
Usual expression: She usually has a sideways smile, with a cool, confident and slightly mischievous attitude.