Who was the first person to suggest that the atom was made up of smaller parts?

i think it may have been john dalton. he discovered the atomic theory... here's some extra info if you need it=

John was born in 1766 of English nationality in Eaglesfield, Cumberland, England. He was an English chemist, physicist and meteorologist. John Dalton is most renowned for his pioneering work in the development of modern atomic theory, and his research into blindness, which is sometimes referred to as Daltonism in his honour. Apparently he never married and he was also colourblind.

hope that helped :)