Wilhelm Conrad Röntgen discovered X-rays quite by accident in 1895, while he was conducting experiments on the properties of cathode rays. He noticed that a fluorescent screen in his laboratory began to glow even when it was not in the direct path of the cathode rays. Intrigued, Röntgen began to investigate this phenomenon further.

He discovered that the fluorescence was being caused by a new type of radiation, which he called X-rays (or "X-strahlen" in German, meaning "unknown rays"). Röntgen realized that X-rays had the ability to penetrate many types of materials, including human tissue, and that they could be used to create images of the internal structure of the body.

Röntgen's discovery was a groundbreaking one, and it quickly captured the attention of scientists and the public around the world. His initial paper on the subject, "On a New Kind of Rays", was published in December 1895, and within months, X-rays were being used in medical applications, such as diagnosing bone fractures and locating foreign objects in the body.

Röntgen was awarded the Nobel Prize in Physics in 1901 for his discovery of X-rays, and his work laid the foundation for the development of medical imaging technologies such as X-ray radiography, computed tomography (CT), and magnetic resonance imaging (MRI). Today, X-ray technology continues to be an essential tool in medicine, materials science, and a wide range of other fields.