Just finished the novel and still untangling my thoughts about the lead. It's not the easiest question because 'Whisper' focuses so tightly on one person's internal world – the unnamed protagonist, a man trying to piece together a childhood memory of a voice he heard once. He's less a traditional 'character' with a job and a backstory and more a vessel for an obsession. The whole book is his internal monologue, a spiral of doubt and fixation as he revisits his hometown, interviews fading relatives, and tries to pin down this ephemeral sound. Calling him a 'detective' feels too active; he's more like an archaeologist of his own senses.
That obsessive quality is what makes him central, though. The plot is entirely driven by his need to know, and his increasing isolation from everyone who thinks he's lost his mind. We see other characters only through the distorting lens of his mission. So while he lacks a name, his consciousness is the entire stage. I found myself equally frustrated and sympathetic, which I think was the point. The ending leaves you wondering if the whisper was ever the point at all, or if the search itself was the only real thing about him.