David Wark Griffith is the man that invented the language of motion pictures. As a clerk in a bookstore in Louisville in 1890, he was exposed to literature and to those who made a living out of it, the actors. He quickly joined them, and even wrote some screenplays. But in 1907, the sale of scenarios to Edwin S. Porter, the director of The Great Train Robbery, got him a place in Biograph, a company churning out one-reelers in the growing Hollywood industry. He directed hundreds of such short films
during the following six years, directing actors such as Lillian Gish or Mack Sennett among many others. It is there that he learned the trade of making movies; yet Porter wouldn't let him shoot longer films, and his frustration made him leave Biograph.
He then bought the right of the novel The Clansman, an epic about the reconstruction in the South after the Civil War. He turned it into a movie, renamed Birth of a Nation after successful prescreenings. This movie was a revolution in film making; whereas pictures were only made of one hundred shots, this one was divided into 1544 different ones. It was the first to successfully combine and master what would essentially become the grammar of cinema for the century to come. He had transformed it from a rather low-brow form of entertainment into an art. The problem was that Griffith, a man of he South, wasn't even aware of his prejudices. His movie became quickly a blockbuster, the first of them all, yet black Americans protested against it: Birth of a Nation is a racist film, promoting the KKK and the "Old South" values...
Angered at the accusations of racism by critics, which he saw as censorship and attacks on his artistic integrity, about a film successful both financially (having cost $140,000 to make, it grossed millions) and artistically (Serguei Eiseinstein and Fritz Lang would name it as a major influence), he made Intolerance as an answer. This film was supposed to be his call for Fraternity and Humanism. It told four stories, one about the fall of Babylon, one about the last days of Jesus Christ, one about the Religious Wars in Europe, and finally a modern story, intertwining them with shots of a woman rocking a cradle, and having the four of them end simultaneously in a thrilling climax. Griffith even spent most of the grossings from Birth of a Nation into the production of this movie, building 100-metres high sets, and using huge crowds. It was again an artistic success. However the movie was too complex for the public, and the film flopped.
For the next ten years, he would alternate between expensive and ambitious films, and cheaper, more profitable and reliable movies, to avoid losing money again. In this too, he was an innovator in Hollywood. In 1919, he cofounded United Artists with Charlie Chaplin, Douglas Fairbanks and Mary Pickford; they wanted to preserve their freedom from the producers, who were gaining power in the industry.
He then made quite a few fine movies, especially when he directed the Gish sisters, such as in Hearts of the World (1918), Broken Blossoms (1919) and Orphans of the Storm (1920). But the sisters then left him, and D.W. Griffith's art was already in its decline. The mainstream Hollywood industry moved ahead of him. He made movies until 1931, even making two talkies, but after that he was unable to find a job. As he got old, he didn't get poor, as he had been wise in his investments, yet he became bitter at the industry which he had created, the medium of which he had invented, but which wouldn't let him work. Orson Welles in 1939, having just been hired for Citizen Kane with almost no conditions, met the ageing Griffith, who had been waiting for such a contract for two decades. The encounter between the inventor of the art of movie making and the one about to transform it was not pleasant.
Information coming from the imdb, the film 100 (www.film100.com), and personal knowledge.