Gerard K. O'Neill was an American physicist and space advocate, best known for his work in the field of space colonization. He founded the Space Studies Institute in 1977, which focused on developing technologies for human settlement in space. O'Neill's vision included the construction of large space habitats, such as the O'Neill Cylinder, which could support human life in orbit. O'Neill was also a professor at Princeton University, where he taught physics and inspired many students with his ideas about the future of humanity in space. His influential book, "The High Frontier," published in 1976, outlined his concepts for living and working in space, promoting the idea that humanity could thrive beyond Earth.