Stephen Falken (John Wood) is one of the main adults of the film who, alongside David Lightman and Jennifer Mack, race against time to prevent Global Thermonuclear War.
Dr. Stephen Falken is a brilliant computer scientist who is responsible for creating and developing artificial intelligence in computers which allow them to learn from their experiences. His greatest achievement was a computer system called "Joshua", which was created for and used by the American military.
Falken's work with the assistance of John McKittrick led to the creation of WOPR, a machine intended to continuously simulate a series of "War Games" in order to predict and calculate an estimation of a possible World War III outcome.
He had a son named Joshua and a wife, who both were killed in an unfortunate car crash. Shortly after his son and wife's death, he came up with the computer program with the same name that ran on WOPR. It's strongly suggested that this accident is what drove Falken to denounce his government work and request a quiet "death" from the United States Department of Defense, for whom he worked for many years.
His alleged "death" was arranged by the United States military at the time he was 41 due to security concerns, right after he had "given up" on humanity. He had been living the remainder of his life under the alias Dr. Robert Hume, on Goose Island, Oregon. He had taken up a new interest, paleontology, however it paralleled his old life. Falken was interested in how dinosaurs lived for eons, only for them to die in one cataclysmic event, and figured humanity was doomed to a similar fate and evolution would begin again. When David Lightman and Jennifer Mack remark that Professor Falken would not be so pessimistic about the world if his wife and son were still alive, he is convinced to return to NORAD with the pair.
While a pessimistic character, Falken had greater knowledge than David; he knew that Joshua would reach the discovery of futility, and ultimately not proceed with actual war.