I don't think so. There are so many fictional characters with immense powers, and it's tough to declare one as the absolute strongest. SCP 3812 is powerful, but there could be others equally or more powerful depending on the context and the rules of their respective universes.
The authors of SCP stories are a mix. Some are known within the SCP community for their consistent and quality contributions, while others might be newcomers sharing their unique ideas. The diversity makes the SCP world rich and engaging.
The main characters in the SCP game story are often the personnel of the SCP Foundation. They are scientists, guards, and agents who are tasked with containing the SCPs.
In the 'scp secret laboratory story', there are the members of the SCP Foundation, such as the scientists and security personnel. They play a major role as they are in charge of dealing with the SCPs. Also, there are the SCP entities themselves which, although not traditional characters in the sense, are central to the story. And then there are groups like the Chaos Insurgency who are antagonists and cause problems for the Foundation's operations.
The SCP Foundation is purely fictional. It's a collection of imaginative and often creepy stories and characters that are made up for entertainment purposes and have no basis in reality.