Caption: Albert Einstein (1879--1955), master of the universe.

Einstein is seen here, chalk in hand, lecturing in Vienna, Austria in 1921.

In the days when he was the supreme master of physics.

Credit/Permission: Ferdinand Schmutzer (1870--1928), 1921 (uploaded to Wikipedia by User:Hemulen, 2006) / Public domain.
Image link: Wikipedia: File:Einstein_1921_by_F_Schmutzer.jpg.
File: Einstein file: einstein_master_1921.html.