Johann Heinrich Lambert was an 18th-century German mathematician, physicist, and philosopher, born on August 26, 1728. He is best known for his work in geometry and his contributions to the understanding of light and optics. Lambert was the first to prove that the number π (pi) is irrational, which means it cannot be expressed as a simple fraction. In addition to his mathematical achievements, Lambert made significant advancements in astronomy and philosophy. He developed the concept of the Lambertian reflectance, which describes how light reflects off surfaces. His diverse contributions have had a lasting impact on various scientific fields.