Dante is the reason that modern Italian was adopted!

When the Roman empire fell, different dialects of Latin developed on the different populations that later made up Italy. The dialect that eventually became modern day Italian can be traced back to famous writer, Dante Alighieri.

His work, the Commedia (later called the Divina Commedia), was so widely read all along the region that it became the 'canonical standard' that all Italians could understand. This meant that the language of Florence, which Dante spoke, became the defacto official language of Italy.

(Source)