The inventor of the handkerchief ...
... was Richard II, or so it would seem.
Some time between 1384 and 1386 a clerk in the Great Wardrobe recorded, (in Latin) the presence of "small pieces of linen made to be given to the Lord King for blowing and covering his nose". Such a careful record certainly suggests an innovation.
By 1395-8 this was old hat: the clerk just recorded the acquisition of "11 portions of linen cloth from Rheims , for clearing the nose of the king".
This suggests either a severe case of catarrh or, more plausibly, that the king was distributing these to courtiers, which well might have made the court a more pleasant place. It was also "consistent with what we know of his earlier distribution of the badges of the white hart".
From G.B. Stow, "Richard II and the invention of the pocket handkerchief," Albion, Vol 27, No 2, 1995. (And no, not what I was supposed to be researching, although I did make a couple of nice small discoveries in that area also.)