"Joseph Priestley was an 18th-century English Separatist theologian, natural philosopher, chemist, innovative grammarian, multi-subject educator, and liberal political theorist who published over 150 works. He has historically been credited with the discovery of oxygen, having isolated it in its gaseous state, although Carl Wilhelm Scheele and Antoine Lavoisier also have strong claims to the discovery.
During his lifetime, Priestley's considerable scientific reputation rested on his invention of soda water, his writings on electricity, and his discovery of several "airs" (gases), the most famous being what Priestley dubbed "dephlogisticated air" (oxygen).
Priestley, who strongly believed in the free and open exchange of ideas, advocated toleration and equal rights for religious Dissenters, which also led him to help found Unitarianism in England. The controversial nature of Priestley's publications, combined with his outspoken support of the French Revolution, aroused public and governmental suspicion; he was eventually forced to flee in 1791, first to London and then to the United States, after a mob burned down his Birmingham home and church. He spent his last ten years in Northumberland County, Pennsylvania.
A scholar and teacher throughout his life, Priestley also made significant contributions to pedagogy, including the publication of a seminal work on English grammar and books on history, and he prepared some of the most influential early timelines. These educational writings were among Priestley's most popular works. It was his metaphysical works, however, that had the most lasting influence, being considered primary sources for utilitarianism by philosophers such as Jeremy Bentham, John Stuart Mill, and Herbert Spencer (Wikipedia)."
Discoverer of Oxygen - Joseph Priestley, Discoverer of Oxygen National Historic Chemical Landmark - American Chemical Society