Jorge Luis Borges
Borges basically founded the magical realism movement. Wikipedia says that the term was used for the very first time to describe one of his earliest works. So there you go.
Borges never wrote a novel. He wrote poetry, essays, and short stories. He wrote short stories about longer stories. He wrote critical assessments of fake novels so that he could get his kicks writing about how cool the concept was without having to write the novel (because he did not believe in himself enough to sit down at write one).
Borges started losing his eyesight in his fifties, and was almost completely blind by the end of his life. He had people read to him. He wrote some magnificent words about blindness. My favorite:
"Blindness is not darkness; it is a form of solitude."
I was introduced to Borges in a math class, of all places. At Sarah Lawrence, almost no one wanted to take math, so the faculty often had to come up with clever outside-the-box classes that would appeal to artistic types. The course was called Mathematics & Jorge Luis Borges, and I had never heard of him, but it seemed really interesting to me, so I took it. We read a ton of his stories and some poems and a few essays, and we talked about his use of mathematical concepts and related it to some seriously interesting theory. That class was formative as fuck. It was like I had found what I never knew I had been looking for, and I suddenly finally knew what I wanted to do with fiction.
Borges wrote about legends and myths and history and literary theory, and he wrote a detective story and stories about books. He utilized the concept of infinity in ways that I will never stop trying to imitate. If you've never read anything by Borges, go find yourself a copy of The Aleph, and read the title piece. Then read some others. Then find some other collections.
Anthony Kerrigan is generally regarded as the best translator. I have full collected works translated by Andrew Hurley, which is passable. I can't speak to the others. Mostly, reading Borges makes me wish I could read in Spanish, because if his work is so unbelievably beautiful in this decidedly unmusical language, I can't even imagine how amazing it must be in the original form.
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