Who was the first to define an element?

Robert Boyle is recognized for being one of the first to provide a definition of an element. In his work during the 17th century, he proposed that elements are substances that cannot be broken down into simpler substances by chemical means. This was a significant step in chemistry as it laid the groundwork for later definitions and understandings of elements in the context of modern chemistry.

John Dalton, while he contributed significantly to atomic theory, did not define what an element is in the way Boyle did. J.J. Thomson is known for discovering the electron and his work with cathode rays but did not focus on defining elements. Ernest Rutherford's contributions primarily revolve around the structure of the atom and radioactivity rather than defining elements. Boyle's earlier contributions are pivotal since they helped to establish the foundation of modern chemistry and the understanding of elements as fundamental substances.