One characteristic is their detailed historical settings. They accurately depict the time period, whether it's the architecture, clothing, or social hierarchies.
Since I don't know the exact Adam Clinton murder mystery novels you're referring to, it's difficult to determine the author. It could be a new author who has chosen to focus on this character. There are so many new voices in the mystery genre these days that it could be someone who is yet to gain widespread recognition.
Cullen Rutherford in fanfiction can be seen in various lights. He's a character that has a strict code due to his templar training. Fanfic writers often play with this. For example, they might write about how he deals with mages in a different way than in the game. His appearance, with his blond hair and those intense eyes, is often described in great detail in fanfictions. Also, his leadership skills are either emphasized or questioned, depending on the plot of the fanfiction. His journey from being a templar to something more, perhaps more accepting of different ideologies, is a common theme.
A third theme could be the life and character of Rutherford himself. It could explore his determination, his relationships with other scientists, and his role in the scientific revolution of his time. It might include his early life, his education, and how he overcame obstacles to make his great scientific achievements.
If Cullen Rutherford is a fictional character, then the interesting facts would depend on the story or context in which he is created. For example, if he is a character in a mystery novel, his interesting facts could be related to his detective skills or his complex backstory. But again, without knowing more, we can't be sure.