Ellinia used to be a fox (Yes a fox). She lived in hill top zone. During the events of sonic 1 Eggman captured her and brought her to his base. (It happend during sonic 1 so sonic didn't know about it!) Ellinia was to big to power a robot, so he decided to conduct a DNA experiment.
He wanted to instert hedgehog DNA into a diffrent speicies without it splicing. And he suceeded.
After the process was done.