Gerard Kitchen O'Neill was an American physicist and space activist. As a faculty member of Princeton University, he invented a device called the particle storage ring for high-energy physics experiments. Later, he invented a magnetic launcher called the mass driver. In the 1970s, he developed a plan to build human settlements in outer space, including a space habitat design known as the O'Neill cylinder. He founded the Space Studies Institute, an organization devoted to funding research into space manufacturing and colonization.
O'Neill began researching high-energy particle physics at Princeton in 1954, after he received his doctorate from Cornell University. Two years later, he published his theory for a particle storage ring. This invention allowed particle accelerators at much higher energies than had previously been possible. In 1965 at Stanford University, he performed the first colliding beam physics experiment.
While teaching physics at Princeton, O'Neill became interested in the possibility that humans could survive and live in outer space.