Iizuka wanted to let people do that to some extent, but it was only until Sonic Forces that Sonic Team acquired the skills, people, and technology to make this possible in a Sonic game. The idea for the Avatar to be a customizable character first began over twenty years ago when Iizuka took notice of all the Sonic-type characters the fans (especially Americans) were creating and sending him via fan-mail.
While a lot of fans wanted more gameplay variety, they still wanted to play as Sonic, so the designers gave this character (which would become the Avatar) the Wispon to give it a unique gameplay style, and movements with emphasis on high-speed running and jumping that made it feel similar to Sonic. According to Takashi Iizuka, the idea for the Avatar came about to make a character with a unique gameplay experience to differentiate them from other characters in the Sonic the Hedgehog series.
