the Last Inkling

the weekly standard has an article on Christopher Tolkien, the last Inkling, who has officially retired at age 94, after editing his father's notes and stories and releasing them for publication in many books, including Unfinished tales of Middle Earth (link link2) , and the History of Middle Earth.

the last of these books was just published, but it was begun during World War I, and of course a shorter version is in the Simarillion.

His links to his father's literature go back to his childhood:

It is work that has spanned Christopher Tolkien’s life. He started editing at just 5 years of age, catching inconsistencies in the stories his father told at bedtime. When those stories became The Hobbit, Christopher’s father promised him tuppence for every mistake he noticed in the text. A few years later, Christopher was typing up manuscripts and drawing maps of Middle-earth.

the article doesn't mention why: Christopher had developed rheumatic fever and was placed on prolonged bedrest. His father did much of his tutoring work at his home office (supervising students) so kept him company in his spare time.