Giacomo di Grassi was an Italian fencing master who wrote the fencing manual Ragione di adoprar sicuramente l'Arme, si da offesa come da difesa in 1570. The text was later translated into English and published again in 1594, as DiGrassi, His True Arte of Defence. Di Grassi was one of the three premiere fencing masters known from Elizabethan England.
His main teachings were that weapons of the same length are used similarly, the thrust is preferred to all other attacks, as well as specifics on how to thrust and handle specific weapons.
Read more about Giacomo Di Grassi: Introduction, Ideal Movements, The Use of Less Perfect Motions, General Tactics, The Shield