Who was Athenian ruler advanced the cause of democracy by taking steps to allow all citizens to participate in their government.

I would say that Pericles was a strong advocate for Athenian democracy though it had been existence before him and he promoted the ability of citizens to participate in the functioning of their government. I would also say that the current Prime Minister or Alexis Tsipras believes in true democracy and a government that really tries to serve the vast majority of the people by refusing to allow the debt to the European Union to overshadow the social needs of the Greek people.