I ran into the following error
Unknown class TutorialViewController.swift in Interface Builder file.
when renaming the default files Main.storyboard and ViewController.swift to my desired naming convention of TutorialView.storyboard and TutorialViewController.swift respectively.
I renamed the files by physically renaming the file names in Xcode and updating the class name of TutorialViewController.swift.
After renaming, I tried to fix the link from TutorialView.storyboard to TutorialViewController.swift by updating the storyboard's Custom Class to TutorialViewController, which is the correct way to complete the link. This in fact caused the above error.
Disclaimer: I'm aware this is similar to this SO post but I wanted to make this question and answer my solution, as that post does not have an accepted answer. I'm hoping I can save someone all the time it took me to figure this out.