Gerald Robotnik kept several diaries during his lifetime, documenting his research and thoughts.
Sonic Adventure 2
In Sonic Adventure 2, Gerald created a diary during his imprisonment at the hands of the Government:
I don't quite know what happened or what went wrong. Was it a mistake to create the ultimate life form? I thought it would be something that would benefit mankind. But then the military guards landed on the colony that day. They were sent to destroy the research project that I had been working on. My colleagues at the research facility, my granddaughter, Maria. I hope you are all safe.
The colony was completely shut down, probably to keep the prototype from falling into the wrong hands. The ARK was shut down under the premise that there had been an accident.
I found Maria's name among those who died when the ARK was shut down. She meant everything to me and I couldn't bear the thought that she died because of my research. I lost everything. I had nothing more to live for…I went insane. All I could think about was to avenge her…somehow, someway. I got scared as I was no longer able to control my thoughts. All I could think about was that I wanted it all to end.
Based on my original projections, I was able to complete my project, Shadow. I designed its mind to be perfect, pure. I will leave everything to him. If you wish, release and awaken it, to the world. If you wish to fill the world with destruction…
In Sonic Rivals 2, it is revealed that Gerald also kept a diary regarding his research on a powerful being named the Ifrit, a terrible creature that exists in another dimension. The following entries has been revealed:
Entry 1: The all powerful Ifrit...
Entry 2: The Ifrit held the power of destruction, and the power to blind one's soul...
How could you possibly believe someone would throw ME into jail?! Union Army Prison? Oh, hell. I am the father of the pseudo-perpetual mobile "Chaos Drive" for christ's sakes. Could this possibly be the sinister conspiracy of those attempting to acquire and take over "Eclipse Cannon" and "Artificial Chaos"? Then I'll show them that I am not going to succumb to such immorality. For the complete picture of the ultimate biosis development project "Shadow" lies only in my mind...
"Revenge, that is all that matters to me now. When I began my research, I only wanted to do good. That's why I worked to make the ultimate creature. But the leaders of the project worried that I'll use it to take over the world. So they seized my lab on Space Colony ARK, then they took Maria from me, and my life took on a new purpose. Instead of helping people, I would get revenge on them. Night and day I've planned, so long after I am gone, my revenge will be complete. I've done it! My greatest design is now complete! The ultimate creature, Shadow. My enemies think they have defeated me, but Shadow will carry out my orders without question. Now it sleeps, but one day it will be reawakened! Shadow will bring total destruction!"
The password for Gerald's diary is "Ma-Ri-A," the name of his granddaughter.
In Sonic Adventure 2, the English subtitles accidentally skip over the mention of "the prototype", which is both heard audibly and written in the on-screen text.