C.S. Lewis used the name N.W. Clerk for the author of the first edition of A Grief Observed.
A Grief Observed was first published in 1961 under the pseudonym N.W. Clerk. Lewis used the disguise because the book records intensely private thoughts following the death of his wife, Joy Davidman, from cancer in 1960.
The work is arranged as a series of reflections rather than a conventional theological treatise. Lewis confronts grief, anger, doubt, memory, and the difficulty of speaking confidently about God while suffering. Its directness distinguishes it from many of his more formal apologetic books.
The pseudonym did not remain permanent. Later editions identified Lewis as the author, allowing readers to connect the book with his biography. N.W. Clerk is therefore the specific answer for the first-edition authorship question, not Lewis’s literary name Jack.