Before his descent, Gerald was a good man and a profound humanitarian, the very much opposite of his psychotic grandson Eggman. He was devoted to using his intellect to help mankind and bring them happiness and hope through the power of science, which he believed was the reason for his existence. While he was much more serious about his work than Eggman, Gerald remained a caring person towards his family. As old age began to catch up to him, though, Gerald would become more forgetful.

Gerald was a man of strong ethical standards, refusing to use his genius for the wrong reasons. He initially refused to lead Project Shadow since he thought obtaining immortality was against nature and because he had no interest in aiding with war. That said, he was not above breaking his ethics for certain reasons, like when being forced by the higher-ups or when he thought it was for the greater good, such as joining Project Shadow or handing over the dangerous Emerl to find a cure for his dying granddaughter. Even when in such situations, however, Gerald went out of his way to make sure his research would have the potential for good as well, like how he gave both Shadow and Emerl genuine feelings and planned to share Shadow with the world to help mankind. He also held the strong belief that power born from the desire to protect rather than the desire to conquer would make all conflicts cease to exist.

When Maria was killed, Gerald went through a profound change, as he was consumed by grief and slowly went insane. He eventually became a rage-filled psychopath, developing a deep hatred for humanity who he blamed for Maria's death, and grew obsessed with revenge by committing global genocide. Even in his last moments, all Gerald had to express was his contempt at humanity, and he died a broken man.

Use whatever voice you feel fits this character.