The cyclotron was invented by Leo Szilard in the early 1900s and accelerated the development of nuclear physics and particle accelerators. It allowed scientists to produce radionuclides for medical imaging like PET scans and treat cancer with proton therapy. Szilard later regretted his role in nuclear weapons and founded the Council for a Livable World to advocate for arms control. The cyclotron continues to be used for fundamental particle physics research and medical isotopes, influencing fields from astrophysics to medicine.