Leonardo da Vinci helps Ezio Auditore in Assassin's Creed II by designing inventions and modifying equipment.
Leonardo becomes one of Ezio's closest allies after the story moves through Renaissance Italy. He translates pages from Altaïr's Codex, improves Ezio's hidden blade, and develops devices that expand the Assassin's capabilities. His workshop also provides a recurring point of contact during the campaign.
The game uses real elements of Leonardo's life while placing him inside a fictional Assassin-Templar narrative. Ezio visits cities including Florence, Monteriggioni, Venice, and Forlì, and Leonardo's work connects the game's historical setting with its science-fiction technology.
Leonardo should not be confused with Michelangelo, another famous Renaissance figure who appears in the broader setting but is not Ezio's technical partner. Raphael and Donatello are also Renaissance artists, but neither fills Leonardo's role in Assassin's Creed II.