Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Ronald Lauder
On June 18, 2006, he purchased from Maria Altmann and her family, the painting "Portrait of Adele Bloch-Bauer I" by Gustav Klimt for $135 million, the highest price ever paid for a painting at that time. Lauder called the painting "Our Mona Lisa". He reportedly saw Klimt's portrait as a youth in Vienna and had admired it since. The painting, a Nazi-looted art piece which had just been restored to Altmann following years of negotiation and litigation with the Austrian government, now forms the centerpiece of the museum's collection.