Who was the first major Italian poet to write in Italian?

The first major Italian poet to write in Italian is generally considered to be Dante Alighieri. While he wasn't the absolute first to use the vernacular, he is credited with elevating the Italian language to a level of literary prestige that had never been seen before.

His masterpiece, "The Divine Comedy," written in the Tuscan dialect, is considered the foundational work of Italian literature and helped establish a standard for the Italian language.

While some others used vernacular languages before Dante, their works did not have the same lasting impact or influence on the development of the Italian language.