John Dalton is best known for pioneering modern atomic theory. Though the idea of atoms has been around for quite some time, Dalton continued countless scientific work and created what is now called Dalton's law.
Dalton established that elements are made of atoms and that they cannot be subdivided or destroyed; however, he noted that atoms can be combined, separated or rearranged in chemical reactions. Dalton's work also theorized that atoms of different elements can combine to form chemical compounds. His legacy has remained intact, and he is credited for the comprehensive development of atomic theory.
In addition to his work with atomic theory, Dalton is also well-known for his research into color blindness. He was afflicted with the condition and attempted to theorize its origins. Though his theory was later proven wrong, color blindness later became to be known as Daltonism because he was the first person to research the subject.