The six-stringed instrument as we know it today, at least we qualify as "Spanish guitar" was devised by Antonio de Torres Jurado, a Spanish builder that this year up to its bicentennial.
Native Almeria, Spain, on June 13, 1817, Torres Jurado established standard measures guitar to the fifties of the nineteenth century, which brought an end to a number of disputes and disagreements among guitarists of the time: the instrument predecessor had a somewhat smaller body, narrower waist, but could be up to ten strings, up to two-masted, double or single ropes, which raised more than a few disagreements between composers and performers, as there were authors who wrote, as Napoleon Coste for seven-string guitar, while others did for other amounts.
So, at the height of the instrument, and in full obsession with making the guitar occupy a place of prestige among the instruments, as already enjoyed the violin and the piano, for example, measures and plans were laid down with which we know as modern guitar or Spanish guitar was standardized.
Of course, it is worth quoting two wonderful performers, as Emilio Pujol and Francisco Tarrega, who had the privilege of playing with instruments Torres Jurado, made by the builder himself.