Who instituted reforms to the Athenian government in 594

b. c. that included a governing body known as the Assembly and people's courts with juries?

I believe that the answer is Solon. He was the one who started and instituted reforms to the Athenian government in 594 B. C. He was selected by the Athenians to revise the laws. Although, the reforms he made was not the real reason for democracy but it was the basis for the current Athenian governement.