Lisa Gherardini

According to the human Mona Lisa animated in the International Gallery, the model of Leonardo da Vinci's painting Mona Lisa was an Italian housewife from the 16th century. When the Mona Lisa came to life in the early 21st century, she called her model a dreary woman who "laughed like a camel and farted like a donkey." The animated painting also asserted that her so-called enigmatic smile was due to her model experiencing flatulence during the portrait sittings. (TV: Mona Lisa's Revenge) Another account indicated that Clara Oswald was the painting's model. (COMIC: The Swords of Kali)

Behind the scenes
Who Was 'Ere!, one of the parodical comic stories in The Doctor Who Fun Book, which took a comedic look at the Doctor's influence on Earth's history and on popular culture and mythology, featured a panel showing the Fourth Doctor bedeviling Leonardo during the painting of the Mona Lisa by offering the unnamed model jelly babies. This constitutes the only appearance of Mona Lisa's model in the flesh in a Doctor Who story (albeit not one considered valid on this Wiki) to date, except, of course, insofar as she may be Clara Oswald. In that story, the Doctor lovingly calls her "Mo", seemingly confirming that her name was in fact Mona Lisa.