Joseph Priestley was an English chemist and philosopher, best known for his discovery of oxygen. Born in 1733, he made significant contributions to the field of chemistry, including the identification of several gases. Priestley's experiments with gases laid the groundwork for modern chemistry and helped to advance the scientific understanding of the atmosphere. In addition to his scientific work, Priestley was also a theologian and a political thinker. He was a strong advocate for freedom of speech and religious tolerance, which often put him at odds with the authorities of his time. His legacy continues to influence both science and philosophy today.