Luis Goytisolo has won the Spanish Premio Nacional de las Letras Españolas [National Prize for Spanish Letters]. I found his Antagonía tetralogy challenging but well worth reading. Sadly, it is not available in English. Indeed, none of his work is available in English. His brother Juan won the prize in 2008. The only other writer on this site who has won it is Ana María Matute, though I hope to get to some of the others in the not too distant future.