Carl is the name of someone who left a letter, presumed deceased. His letter reads:
If you are reading this, I am dead. Now, don't get all sad and emotional about it! It was probably a very, very long time ago. Name's Carl, and I have a very important request for you: restore Ravenskye City! As you can see, it's all covered in vines and ruins, and the totems are all in a deep sleep. As an added bonus for restoring the City, you'll hear all about some ancient prophecy from yours truly!
Behold! Another letter from Carl! (That's me, remember?) If you got this, that means you've improved the City! Great job with that! I'm sure it looks lovely. It also means that my whole magic scroll system is set up properly. Maybe you ARE the builder that prophecy spoke of. By any chance, did you happen to crash land in Ravenskye on an airship? That would be a good sign.