I guess this was mainly a Continental thing, but for a while philosophers often wrote novels that in some way expounded their philosophy. I think Nietzsche was perhaps one of the earliest, with Zarathustra. All the French existentialists wrote novels, too. What happened to this trend?
EDIT: I just realised that arguably this goes back all the way to Plato! But I was thinking less of straightforward, largely plot-free dialogues and more of full fledged novels, like Sartre’s Nausea.
I would argue any good faith fictional novel is in and of itself an expression of a philosophy held by the author. The words and phrases one chooses to describe the scenery, characters, and plot come from their experiences of the world. The themes that appear can be regarded as the author’s philosophical approach to the situations. By good faith I mean a novel written with the intent of communicating a story or idea, not one written out of pure intent to profit.
Consider the, now somewhat cliche, author George Orwell. Though not a philosopher by trade, the collective themes of his novels revolve around the causes and effects of totalitarianism (a political philosophy). Yet clearly the presentation of his works is not in an objective manner, he is not presenting mere facts about totalitarian regimes. He uses a strong negative connotation, and uses the idea it is something to be avoided. This implies a political philosophy of anti-totalitarianism. I think you could make a similar argument for modern popular author’s like John Green.