I have often wondered about this, and never been able to make up my mind until today - the answer is Owen Barfield.
The reason is that I have been reading This Ever Diverse Pair, which is usually (misleadingly) billed as a novel but which is a fictionalized autobiography, mostly describing the relationship between Barfield's real self and his public persona as a drudging solicitor.
The atmosphere of this book is mostly light and comedic, but the sheer horror of the mundane situation of Barfield in legal practice struck home to me by analogy with the (relatively short) times when I was a proper doctor - i.e. a house officer ('intern'), a psychiatrist, and a public health physician; and how utterly alien I found these situations: how strongly at odds with my deepest being.
I couldn't really recommend this book, especially as it ends so badly (I think Barfield has a serious, recurrent problem with the difficult art (rarely achieved) of ending books well: he is bad at it) - but it was memorable to me for the above reason and for the powerful personal identification it yielded with Barfield: more powerful than I have ever felt for any other of the Inklings.
Having made this identification it suddenly seems quite obvious - in that I am a non-fiction writer, and indeed an essayist, at heart (like it or not, that is what I am) and secondarily a lecturer... which is pretty much exactly what Barfield was (like it or not).