These are letters from Naron — a D’ni exile (a child during the Fall) who has lived among humans on the surface world for some 250 years and who has recently returned to the Cavern — to family members (principally his mother, Lendi) who remained in Kedross, the family Age to which they fled after the Fall. They appear here translated into English from the D’ni originals.
Naron currently goes on the surface by the name “Ron Bournewold”; other names have been used in the past, though this scholar is only aware of “Ron Dinesen,” the name under which he served in the US Army in World War II.
As yet unknown is how precisely he returned to the Age of D’ni (i.e., Earth) from his initial exile on Kedross (it appears he has at least enough skill in Writing to create linking books from various points on Earth’s surface, and probably also wrote the linking book he uses to return to Kedross).