Freeman Dyson loves the metaphor that divides scientists into two groups: Birds, who look down upon everything and have a God's-eye view of the world, and frogs, who spend their time in the mud. The renowned Princeton physicist calls himself a frog. "I'm not against the first group, but they take an exalted view of science. Frogs typically enjoy exploring things locally and developing skills."

The brilliant frog has spent his lifetime developing skills in disciplines ranging from nuclear engineering to science writing. But he is probably better known to the digerati as the father of computer consultant extraordinaire Esther Dyson. Nonetheless, the slightly built Freeman Dyson is a giant among scientists, largely due to his talents as a writer.

His work as an interpreter of science for the general public has brought many rewards, the first of which is a body of work that includes the autobiographical "Disturbing the Universe" (1979), a meditation on nuclear disarmament, "Weapons and Hope" (1984) and a road map for the most important technologies of the coming century, "The Sun, the Genome, and the Internet" (1999). Dyson's writing has been widely praised for its poetry and artistry, and in 1996 he received the Lewis Thomas Prize, a Rockefeller University-sponsored award that recognizes scientists for their artistic achievements. The key to Dyson's life is that he has never been one to shy away from new experiences. Recalling that his real life began at age 45, when he published his first book, Dyson mused in 1992: "So long as you have courage and a sense of humor, it is never too late to start life afresh."

Born in 1923 in Crowthorne, Berkshire, in south England, Dyson grew up as "a mathematically inclined child born into a musical family ... without pretensions to scientific fame." The Dyson home was rich in cultural and artistic influences. His father, the composer/conductor Sir George Dyson, eventually became the director of the British Royal College of Music in London. Dyson's mother, Lady Mildred, a lawyer by training, was intensely interested in literature and language. Dyson recalls that his parents expressed their affection by encouraging him to explore arts and culture; they were in their early 40s when they started their family: "[Being raised by my mother and father] was more like being with grandparents than parents, but they certainly loved us in their own fashion. It was more intellectual than physical."

Missing from Dyson's boyhood home were scientific influences, until the family adopted one -- Sir Frank Dyson, Astronomer Royal. He was no relation to the Berkshire Dysons, but he was from the same part of Yorkshire as Sir George Dyson. In his 1992 book "From Eros to Gaia," Freeman Dyson recalls that the breakfast table discussions between his father and other relatives about Sir Frank's exploits heavily influenced his early interest in astronomy and spurred him to take up his pen as a 9-year-old and write a novel based on the activities of Sir Frank.

The unfinished manuscript of "Sir Phillip Robert's Erolunar Collision" is at once a snapshot of the astronomical events of 1931 and a window into a future project that would occupy a good portion of Dyson's professional ruminations: space travel. It's also a good satire of large-scale science projects. In 1931, the orbit of asteroid Eros was going to pass close to the Earth, providing an important opportunity for astronomers to get an accurate reading of the distance between the Earth and the sun. In the incomplete novel, Sir Phillip, director of the British South African Astronomical Society and a character based on Sir Frank, successfully predicts an Erolunar collision by calculating the orbit of Eros 10 years and 285 days in advance.

Dyson turned to one of his science-fiction heroes to help the plot along. The characters decide to rewrite the mission described in Jules Verne's "From Earth to the Moon and a Trip Round It" to change Eros' destination to go directly to the moon and land the astronomers on its surface to witness the collision. Then reality crept into Dyson's fiction: The astronomical society needed money. Sir Phillip spends the final pages of the manuscript trying to raise funds and design a spacecraft. The novel ends before Sir Phillip can leave Earth.

The unfinished novel proved prophetic. That obviously bright and perceptive 9-year-old grew into a scientist who would consult for NASA and work on numerous government-related projects. In the end, the grown scientist would come away with an opinion that was eerily close to that of the aspiring science-fiction author: that large, bureaucratic-run scientific endeavors often exist to justify their own importance. Dyson assessed his early views in "From Eros to Gaia:" "These observations show that the practice of science has changed less than one might have expected between 1933 to 1991."

Dyson's adult journey began with a stint in the Royal Air Force's bomber command in World War II, a role the Gandhian pacifist took after giving serious consideration to being a conscientious objector. After two years in the service, Dyson attended Cambridge University where he completed a bachelor of arts degree in theoretical mathematics in 1945. In 1947, he made his first trip to the United States to Cornell University to serve a scientific apprenticeship at the elbows of the some of the greatest minds in physics.

Cornell in 1947 was the center of a renaissance of pure physics research, born of the ideas and concepts that had lain dormant during the war. One of the chief orchestraters of this rebirth was Dyson's graduate advisor, Hans Bethe, a future Nobel Laureate who spent the war years working on the atom bomb at Los Alamos. Bethe brought other former Los Alamos scientists to Cornell, including Richard Feynman, a young professor of physics who would help influence the course of Dyson's career.

Feynman was then working on a private version of quantum theory that would later become the standard method for making calculations in particle physics. It is a credit to Dyson's scientific acumen and personable nature that Feynman and the other physicists accepted the young graduate student as a colleague straight away. When Dyson wasn't hard at work on a physics problem Bethe had given him, he was part of a coterie of faculty and grad students ministering to Feynman. By spending a lot of time around Feynman, Dyson got the opportunity to observe the physicist "at the height of his creative powers." Dyson understood Feynman's work well enough that he was able to do something Feynman couldn't: write about the theories for a broader audience, a skill Dyson would develop into a second career.

Dyson's work at Cornell was short; his program lasted nine months. But during his studies at the Ithaca campus, he raised many philosophical questions for which his advisor had no answer. Philosophy questions in physics were the bailiwick of another one of Bethe's former Los Alamos colleagues, J. Robert Oppenheimer, who was then director of the Institute for Advanced Study at Princeton. Bethe spoke to Oppenheimer about Dyson, and Dyson was off to Princeton in the fall of 1948 for a year of post-graduate work at the Institute for Advanced Study.

Dyson impressed the legendary Oppenheimer enough with his work that he earned a long-term membership to the institute. Dyson also met his future wife during this time. They married, settled into Princeton, and started a family that grew to six children. By 1953, Dyson had earned an appointment as a physics professor at Princeton's Institute for Advanced Study, a position he held until his retirement in 1994.

After becoming a U.S. citizen in 1957, Dyson caught wind of a fascinating project taking shape near the sun-kissed beaches of San Diego. The Orion Project would allow Dyson to marry his boyhood fascination with Jules Verne to his desire to use his mathematical training to solve an interesting problem: Is it possible to create a propulsion system that will allow man to explore the entire solar system for a politically acceptable cost? Orion provided the most exciting and happiest times of Dyson's scientific life, mostly because he became an engineer, a being apart from a scientist. He noted the difference in "Disturbing the Universe": "There are no prima donnas in engineering. In Project Orion ... nobody was working for personal glory ... It did not matter who invented what."

Orion was born at the General Dynamics Corporation, the progeny of several former Manhattan Project scientists and Dyson, all of whom were anxious to find a more noble and peaceful use for nuclear power. Under Orion, a vehicle much larger than Apollo (perhaps as big as a city) would be propelled into space by several repeated nuclear explosions. The craft would carry a large supply of bombs and the requisite machinery for throwing them out at the right time and location.

Dyson saw so much promise in this project that he predicted to writer John McPhee that they would put men on Mars by 1965 and on Saturn by 1970. Unfortunately, Orion met the same fate as Dyson's fictional Erolunar mission: It never made it to the launch pad and was declared dead in 1965. In his own post-mortem of the project in a 1965 Science article, Dyson attributed Orion's demise in part to politics over funding and by the scientific community's disdain for engaging in anything related to engineering. But mostly, Orion was scrubbed because the Nuclear Test Ban Treaty of 1963 outlawed it. Proponents of the treaty, he said at the time, didn't give Orion a chance.

Eventually, Dyson's own position on nuclear test bans would change: He grew to believe that if the U.S. were to stop nuclear weapons testing and production, it would reduce incentives for the Soviets and others to pour time and money into developing their own weapons. In the early 1960s, Dyson become a staff member of the U.S. Arms Control and Disarmament Agency, where he took part in test ban negotiations. Later in the decade, Dyson chaired the Federation of American Scientists, an organization founded in 1945 as the Federation of Atomic Scientists by former Manhattan Project scientists, including Oppenheimer, for the purpose of addressing the dangers and implications of the nuclear age. Dyson later struck an intellectual balance between opposing views: He became a champion of anti-nuclear activists, understanding at the same time why the government military machine would dismiss the protests.

In his 1984 work "Weapons and Hope," Dyson explained the military's stance toward the anti-nuclear movement with a story from his own childhood. At the age of 7, he took part in a group teasing of a younger child. His mother admonished his actions by telling the young Dyson: "You do things together which not one of you would think of doing alone."

Dyson translated his mother's lesson to fit what he believed was happening between the military and anti-nuclear activists: "Wherever one looks into the world of human organization, collective responsibility brings a lowering of moral standards. The military establishment is an extreme case, an organization which seems to have been expressly designed to make it possible for people to do things together which nobody in his right mind would do alone."

What sets Dyson apart among an elite group of scientists is the conscience and compassion he brings to his work. One of his specialties is in the field of adaptive optics, work with mirrors that can, in theory, allow a ground-based telescope to see objects as clearly in the sky as a space-based telescope. Dyson understood the dark side to adaptive optics -- that the technology used peacefully by astronomers could be used by military to focus laser beams on satellites, aircraft and other targets. Before beginning his work on the optics, Dyson studied both the peaceful and the military applications and determined that the latter death ray scenario was more the stuff of science fiction than reality. To this day, Dyson's work is enabling astronomers to make successful observations.

Dyson is so well-known for his theories about taking Jupiter apart to build a star-bound biosphere (known throughout science fiction as a Dyson Sphere), that it's easy to overlook his physics work, which would earn him worldwide recognition -- membership in the national science academies in three countries including the United States -- and numerous scientific awards, including the 1994 Enrico Fermi Award, given by the U.S. government for excellence in physics. For his own part, Dyson takes a whimsical view of his place in science. He told Omni Magazine in 1978: "It's amusing to think that someday all my 'serious' work will probably be a footnote in a textbook, when everybody remembers what I did on the side."

One could look at Dyson's life and see it as a series of threads, each representing a project he has taken up on the side, all woven together to tell his story. The latest thread concerns Dyson's role as an author, writing about the aesthetics of science and explaining the philosophical and theoretical issues involved in scientific endeavors ranging from nuclear research and space travel to solar power and genetic engineering. In each of his books and articles, Dyson intersperses scientific explanation with meditation on humanism and how the human condition affects science, and vice versa. One of the most eloquent examples of this is in "Disturbing the Universe," where he examines the motivations behind the political actions of the chief architects of the atomic and hydrogen bombs, Robert Oppenheimer and Edward Teller:

Oppenheimer was driven to build atomic bombs by fear that if he did not seize this power, Hitler would seize it first. Teller was driven to build hydrogen bombs by the fear that Stalin would use this power to rule the world. Oppenheimer, being Jewish, had good reason to fear Hitler. Teller, being Hungarian, had good reason to fear Stalin. But each of them, having achieved his technical objective, wanted more ... Each of them became convinced that he must have the political power to ensure that the direction of the enterprise he had created should not fall into hands that he considered irresponsible.

Dyson is a credible analyst because he is a man who has tasted war, having served in the British military while wrestling with his conscience over the morality of war and all that goes with it. In making his observations, he thinks with his heart and hands, qualities he values as an essential part of sound scientific inquiry. This thinking is also an essential part of art. So it is no surprise that Dyson equates scientific inquiry with craftsmanship. Perhaps this is the self-styled frog's greatest legacy: to be down in the mud, engaging in the tactility of life as a human who happens to be a scientist.