Gian Giacomo Caprotti da Oreno, nicknamed Salai or Il Salaino ("The Little Unclean One" i.e., the devil), entered Leonardo's household in 1490. After only a year, Leonardo made a list of his misdemeanours, calling him "a thief, a liar, stubborn, and a glutton", after he had made off with money and valuables on at least five occasions and spent a fortune on clothes.[67] Nevertheless, Leonardo treated him with great indulgence, and he remained in Leonardo's household for the next thirty years.[68] Salai executed a number of paintings under the name of Andrea Salai, but although Vasari claims that Leonardo "taught him a great deal about painting",[69] his work is generally considered to be of less artistic merit than others among Leonardo's pupils, such as Marco d'Oggiono and Boltraffio. In 1515, he painted a nude version of the Mona Lisa, known as Monna Vanna.[70] Salai owned the Mona Lisa at the time of his death in 1525, and in his will it was assessed at 505 lire, an exceptionally high valuation for a small panel portrait.[71]
In 1506, Leonardo took on another pupil, Count Francesco Melzi, the son of a Lombard aristocrat, who is considered to have been his favourite student. He travelled to France with Leonardo and remained with him until Leonardo's death.[14] Melzi inherited the artistic and scientific works, manuscripts, and collections of Leonardo and administered the estate.