Empedocles was a Greek philosopher and poet from the city of Akragas in Sicily, who lived around 495 to 435 BCE. He is best known for his theory of the four classical elements: earth, water, air, and fire. Empedocles proposed that these elements combine and separate under the influence of two opposing forces he called Love and Strife. In addition to his contributions to philosophy, Empedocles is also recognized for his work in natural science. He is often credited with early ideas about evolution and the concept of the unity of all living things. His writings, particularly the poem "On Nature," explore the relationship between the elements and the cosmos.