What is the origin of democracy?
The origins of democracy can actually be traced. The people who started democracy were the Greeks. In fact, if we break up the word, democracy, we can see the Greek derivation. Democracy comes from demokratia, from demos "the people" + kratia "power, rule."
The ancient Greeks were an interesting group of people. On account of the mountainous terrain, the Greeks never formed an empire. Instead, the Greeks formed a compilation of many city states (poleis). By the time of the 5th century BC, there were over 1,100 city states. These cities were independent and were able to experiment with different forms of government. Some cities embraced oligarchies, others embraced tyrannies, and still others formed democracies. Athens is the notable democracy.
The Athenians formed a system in which citizen (male adults) voted on legislation and executive bills. The three pillars were: the Assembly, the Council of 500 and the People's Court. All of these were open to citizens. The only position that was not democratic (that is by lottery) was the position of general for obvious reasons. The person who started this process was Solon, the great lawgiver, and the person who enhanced it was Cleisthenes. The person who brought it to its logical end was Pericles.
Under Pericles, Athenians were paid for service in public office and jury duty. This allowed all citizen to engage in public office even more so.
I know that some will say that women were excluded (and they were) and that Athenians had slaves (and they did), but to the best of our knowledge, democracy started with the Athenians. For this, they deserve our praise.