Louis Harold Gray was a British physicist known for his significant contributions to the field of radiation biology. Born on December 15, 1905, he played a crucial role in understanding how radiation affects living organisms, particularly in the context of cancer treatment. His research laid the groundwork for advancements in radiotherapy. Gray is perhaps best known for developing the concept of the radiobiological effectiveness of different types of radiation. He also contributed to the establishment of the Gray unit, a measure of absorbed radiation dose, which is still used today in medical and scientific applications. He passed away on August 5, 1965.