This is an excellent article to read. Rembrandt Harmensz van Rijn broke with tradition and painted exactly what he saw. He painted to reflect reality, not to flatter his patrons:
For the art historian Taco Dibbits, director of collections at the Rijksmuseum, the answer lies in Rembrandt’s ability to penetrate to the core of his subject, no matter who or what he was painting. “Over the centuries, Rembrandt has inspired artists in different ways,” Dibbits tells me. “Something that has fascinated a lot of artists is the way he depicts different humours, different moods, different psychologies. There is such depth to his personalities: the essence of his genius is that rather than trying to make people more beautiful than they are, he depicts them as they really are. That makes his portraits immensely humane and approachable – unlike, say, classic Italian portraits, which are far more aloof and less direct. Rembrandt didn’t try to please his subjects or the viewer. With Rembrandt, you are looking at real people.”
Think of that when you read about how awful someone's portrait looks. Perhaps it is supposed to look bad. People often look like hell when you consider that much of what goes into our modern culture--plastic surgery, chemical-based makeup, flattering lighting techniques, Photoshop--exists solely to hide nature. Rembrandt was unafraid to show the world that looking like hell wasn't the worst thing in the world.
Can you really say that Rembrandt was the father of modern art? His techniques were revolutionary but it took centuries for the ideas to really take hold.