Corradin

Corradin was the thief (in both Assassin's Creed: Renaissance and Assassin's Creed II) that stole money from Ezio Auditore, prompting the young Assassin to chase him during Ezio's first re-visit to Florence shortly after he and his uncle, Mario Auditore led the successful assault on San Gimignano to assassinate the young Templar (and Ezio's rival) Vieri de' Pazzi. It is revealed shortly thereafter that the thief was actually sent by the Thieves Guild leader (and Ezio's fellow Assassin) La Volpe, who states to Ezio later that although it would've been amusing to watch Ezio seek him out alone, they had little time and so he had sent Corradin to "fetch" Ezio.

Corradin was implied to be just a few years younger than Ezio Auditore and was very polite -yet frightened of- the young Assassin. The young thief also proved instrumental in both Ezio's finding of La Volpe, as well as -in the longer view- Ezio's assassination of Francesco de' Pazzi and saving of Lorenzo de' Medici.

Trivia

 * Were it not for Corradin having led Ezio to La Volpe, the events of the sequence where the young Assassin kills Francesco and saves Lorenzo might have turned out quite differently.
 * In Assassin's Creed: Renaissance, Corradin is tackled by Ezio at Via Sant'Angelo and nearly threatens the young thief for the location of La Volpe, however in Assassin's Creed II, Ezio is ultimately unable to keep up with Corradin and La Volpe shows himself with a laugh, tossing Ezio his money back.