Anthony van Dyck, Portrait of Peeter Stevens (c.1590-1668), 1627
In 1627, the Antwerp cloth merchant Peeter Stevens had his portrait painted by Anthony van Dyck. When Stevens got married a year later, he commissioned Van Dyck to paint his wife Anna as well. Anna was placed on the left, so that Stevens did not have his back turned to her. But actually convention dictated that the man should hang on the left and the woman on the right.
After Rubens, Van Dyck was the most important portraitist of his day. He was popular because he made his patrons look just a bit more beautiful and elegant than they really were.