Critias

Critias (c. 460-403 BC), son of Callaeschrus, was an Athenian philosopher, playwright, and oligarch. He was part of a wealthy, aristocratic Athenian family; his nephew was Plato. He is most noted for being the leader of the Thirty Tyrants, an oligarchic government established in Athens after their defeat in the Peloponnesian War.

In Against the Mathematicians, Sextus Empiricus attributes the Sisyphus fragment (or the Critias fragment) to Critias. In it, he describes the gods as being invented by wise men in order to make their fellow citizens more docile.

  "A time there was when disorder ruled
   Human lives, which were then, like lives of beasts,
   Enslaved to force; nor was there then reward
   For the good, nor for the wicked punishment.
   Next, it seems to me, humans established laws
   For punishment, that justice might rule
   Over the tribe of mortals, and wanton injury be subdued;
   And whosoever did wrong was penalized.
   Next, as the laws held [mortals] back from deeds
   Of open violence. but still such deeds
   Were done in secret,--then, I think,
   Some shrewd man first, a man in judgment wise,
   Found for mortals the fear of gods,
   Thereby to frighten the wicked should they
   Even act or speak or scheme in secret.
   Hence it was that he introduced the divine
   Telling how the divinity enjoys endless life,
   Hears and sees, and takes thought
   And attends to things, and his nature is divine,
   So that everything which mortals say is heard
   And everything done is visible.
   Even if you plan in silence some evil deed
   It will not be hidden from the gods: for discernment
   Lies in them. So, speaking words like these,
   The sweetest teaching did he introduce,
   Concealing truth under untrue speech.
   The place he spoke of as the gods' abode
   Was that by which he might awe humans most,--
   The place from which, he knew, terrors came to mortals
   And things advantageous in their wearisome life--
   The revolving heaven above, in which dwell
   The lightnings, and awesome claps
   Of thunder, and the starry face of heaven,
   Beautiful and intricate by that wise craftsman Time,--
   From which, too, the meteor's glowing mass speeds
   And wet thunderstorm pours forth upon the earth.
   Such were the fears with which he surrounded mortals,
   And to the divinity he gave a fitting home,
   By this his speech, and in a fitting place,
   And [thus] extinguished lawlessness by laws."
   (source: The Critias fragment)