The paintings include one of his most famous works, a portrait of Mrs Altmann's aunt, Adele Bloch-Bauer.

BBC: NEWS | Europe | Austria told to return Klimt art

Besides marking his birth as a collector, that year was also critical because of a chance encounter in Vienna: his first meeting with Adele Bloch-Bauer I.

FORBES: Ronald Lauder: Billionaire Art Collector

Among the pictures are two famous portraits of Adele Bloch-Bauer.

BBC: NEWS | Entertainment | Looted Klimts returned to owner

In 2006, after years of litigation, five paintings by Klimt once owned by Ferdinand and Adele Bloch-Bauer, two Austrian-Jewish collectors who were the painter's contemporaries, were returned to their heirs by Vienna's Belvedere museum.

ECONOMIST: Gustav Klimt

When Adele died in 1925, she left a will asking her husband, Ferdinand Bloch-Bauer, to leave the works to the Austrian Gallery upon his death.

BBC: NEWS | Europe | Austria told to return Klimt art