While some characters like Sonic, Tails, and Knuckles are based on real animals (hedgehogs, foxes, and echidnas respectively), others are entirely fictional.
Here are a few examples:
* Dr. Eggman: A mad scientist with a robotic body.
* Amy Rose: A pink hedgehog with a hammer, who is a very human-like character.
* Shadow the Hedgehog: A black hedgehog with a human-like appearance and personality.
* Metal Sonic: A robotic replica of Sonic.
So, while many Sonic characters have animal inspiration, they are not all real animals. Some characters are human-like or entirely fictional.