Ezio is the first name of the Florentine Assassin who becomes the hero of Assassin's Creed II.
Ezio Auditore da Firenze begins the game as a young nobleman in Florence during the Italian Renaissance. After his family is executed through a political conspiracy, he is drawn into the conflict between the Assassins and Templars. His journey takes him across several Italian cities, including Florence, Monteriggioni, Venice, and Forlì.
Assassin's Creed II introduced Ezio as a more developed protagonist than Altaïr, with a longer personal story and a progression system built around equipment, abilities, and alliances. Leonardo da Vinci assists him by designing and improving tools, including a hidden blade and a flying machine.
Ezio's story continues in Assassin's Creed: Brotherhood and Assassin's Creed: Revelations. Because those games also feature him, the broader character name is Ezio Auditore, while this question asks for his first name only.