The American theoretical nuclear physicist Professor John Wheeler had a singular reputation in modern physics, ranking with Robert Oppenheimer and Edward Teller. With the other two, he played a crucial part in the development of the atomic bomb as a member of the Manhattan Project during the Second World War. As a theoretical nuclear physicist on the project, he was regarded by his colleagues as the equal of Oppenheimer and superior to Teller. Some even believe that he was the “father of the H-bomb”, a title usually reserved for Teller.

He made many contributions to theoretical physics but is perhaps best remembered for a paper written with the Danish physicist Niels Bohr in 1939. Earlier that year, Otto Hahn and Fritz Strassman had demonstrated nuclear fission by bombarding uranium with neutrons. The nuclear age was born.

Soon afterwards, Lise Meitner and Otto Frisch showed that fission occurred because the neutron was captured by the nucleus of a uranium atom, causing the nucleus to vibrate strongly. During the vibrations, the nucleus takes the shape of a dumbbell. The nucleus then splits into two pieces that fly apart.

Hahn and Strassman demonstrated that a fission event releases energy but also emits additional neutrons that could be used to produce fission in other uranium nuclei. The idea of a self-sustaining fission chain reaction producing a very large amount of energy was born. This energy is used in a nuclear weapon to produce a very powerful explosion. It is also used in a nuclear-powered reactor to produce electricity.

John Wheeler worked with Bohr in the late 1930s on the structure of the nucleus and nuclear fission. They co-authored a famous comprehensive analysis of the mechanism of the fission process just before the Second World War started in September 1939. The first steps to the atomic bomb had been made.

John Archibald Wheeler was born in 1911 in Jacksonville, Florida, the son of two librarians. As a boy he lived on a farm in Vermont. He was educated at Baltimore City College, Maryland, and Johns Hopkins University, Baltimore. He received his PhD in 1933.

He was a National Research Council Fellow, working in New York and Copenhagen, between 1933 and 1935. In 1935 he was appointed associate professor of physics at the University of North Carolina and in 1938 he moved to Princeton University as an associate professor.

In 1942 Wheeler joined the Manhattan Project, working at Chicago University and Hanford, Richland, Washington. He worked on the reactor (then called “a pile”) built on the squash court at the Chicago campus that showed for the first time how plutonium, a man-made element, could be produced from naturally occurring uranium. Plutonium was used in the atomic bomb dropped on Nagasaki on August 9, 1945.

Wheeler returned to Princeton University in 1945. He became Professor of Physics in 1947 and the Joseph Henry Professor of Physics in 1966, a post he held until 1976. Between 1976 and 1986 he was Professor of Physics at the University of Texas in Austin.

From 1951 until 1953 he directed Project Matterhorn, a secret project exploring the use of nuclear fusion in building the first thermonuclear weapon (H-bomb). Matterhorn evolved into the Princeton Plasma Physics Laboratory that worked on the development of a nuclear fusion reactor.

At Princeton Wheeler collaborated with Albert Einstein. He tried to achieve Einstein’s project of a unified field theory, a comprehensive theory that would relate the four different types of forces that can occur between bodies. Together, they account for all the observed forces that occur in the Universe.

In the 1950s Wheeler took up a study of relativity and gravitation. In the 1960s he evolved the so-called geometrodynamics, which aimed at the physical reduction of every physical phenomenon, such as gravitation and electromagnetism, to the properties of a space-time. However, geometrodynamics failed to explain some important physical phenomena and Wheeler abandoned it in the 1970s.

But he maintained a long-term interest in the development of quantum theory; he expressed this interest in his influential co-authored book Quantum: The Theory and Measurement. He had a rare talent for making dry, mathematical subjects lively and a colourful way of presenting them.

Wheeler’s work was responsible for much of our knowledge about the strange objects called black holes; he gave them their name. A black hole is an object in space formed by the gravitational collapse of a massive star at the end of its life. It is so dense, and thus its gravitational field so powerful, that nothing, not even light, can escape from it. It will attract and capture matter in its vicinity.

Wheeler’s pioneering work on black holes encouraged scientists, including Stephen Hawking, to develop it. Wheeler wrote a number of books, including: Gravitation: Exploring Black Holes, an introduction to general relativity; Spacetime Physics, an introduction to special relativity; At Home in the Universe; and A Journey into Gravity and Spacetime. He received many honours, medals and awards from a number of countries. In 1995 he was elected a foreign member of the Royal Society.

Wheeler certainly made considerable contributions to modern physics but he did not receive the credit he deserved during his lifetime. He was one of the giant intellects of the 20th century. Many physicists believe that his pioneering work should have earned him a Nobel prize.

The tendency to underrate him may have been due to some extent to his flamboyant style. For example, at one of the annual meetings of the American Association for the Advancement of Science he participated in a session on parapsychology and extrasensory perception. Some of his colleagues were not impressed with this, even though he gave a talk about how insubstantial the evidence for such things is.

Wheeler also made a major contribution through the achievements of the physicists whom he trained and influenced. Among them are Philip Anderson, Richard Feynman and Kip Thorne. Some became Nobel laureates. Modern physics owes much to Wheeler.

His wife, Janette, died last October, aged 99, and he is survived by their son and two daughters.

Professor John Wheeler, nuclear physicist, was born on July 9, 1911. He died on April 13, 2008, aged 96