The sitter’s mysterious smile and her unproven identity have made the painting a source of ongoing investigation and fascination. There has been much speculation and debate regarding the identity of the portrait’s sitter. Scholars and historians have posited numerous interpretations, including that she is Lisa del Giocondo (née Gherardini), the wife of the Florentine merchant Francesco di Bartolomeo del Giocondo, hence the alternative title to the work, La Gioconda. That identity was first suggested in 1550 by artist biographer Giorgio Vasari.

Another theory was that the model may have been Leonardo’s mother, Caterina. That interpretation was put forth by, among others, Sigmund Freud, who seemed to think that the Mona Lisa’s mysterious smile emerged from a—perhaps unconscious—memory of Caterina’s smile.

A third suggestion was that the painting was, in fact, Leonardo’s self-portrait, given the resemblance between the sitter’s and the artist’s facial features. Some scholars suggested that disguising himself as a woman was the artist’s riddle. The sitter’s identity has not been conclusively proven. In an attempt to settle the debate, art and forensic experts in August 2013 opened the tomb of the Giocondo family in Florence in order to find Lisa del Giocondo’s remains, test her DNA, and recreate an image of her face.

Whatever the sitter’s identity, the influence of the Mona Lisa on the Renaissance and later times has been enormous. The Mona Lisa revolutionized contemporary portrait painting. Leonardo’s preliminary drawings encouraged other artists to make more and freer studies for their paintings and stimulated connoisseurs to collect those drawings. Through the drawings his Milanese works were made known to the Florentines. Also, his reputation and stature as an artist and thinker spread to his fellow artists and assured for them a freedom of action and thought similar to his own. One such painter was the young Raphael, who sketched Leonardo’s work in progress and adopted the Mona Lisa format for his portraits; it served as a clear model for his Portrait of Maddalena Doni (c. 1506).

The Mona Lisa demonstrates this aspect of his treatise perfectly in that La Giaconda is dressed in a coloured shift, loosely pleated at the neck, instead of the tight clothes that were then popular.  

Leonardo Da Vinci 

According to www.britannica.com