The Silent Moons were originally a banking and investment company called "Lunar Banking & Co." They were the most powerful and well known banking company on Earth, before The Purge. They appear as short (roughly 4'5" tall) light grey/purple skinned cyclops-like creatures with long elvish pointy ears. They were personally selected by Håågen Dazs himself as his chosen people.
Pre-Purge, the Silent Moons were wealthy bankers, working under the company name "Lunar Banking & Co." , people of dollars and influence, they usually wore a typical black suit, and it was rare that any one of them ever carried a firearm (after Corvo Atano became President of the United States and employed them in his government, they began carrying weapons much more often). Their company gained popularity for the main reason that their competition would always "coinidentally" go out of buisiness, the real reason was that the Moons' CEO would hire hitmen to eliminate the opposing company's boss, but no one knew. Post-Purge, the Silent Moons, driven insane by the loss of all their wealth (and the radiation), they sought salvation in the God of Wealth, Håågen Dazs. Dazs used their insanity to his advantage, and enslaved them, but lied to them, telling them they were his "chosen people". This was only supported by Grand Cardinal Estarmo VI, who insisted to his bretheren that Håågen Dazs wished only the best for them. After Blue Team defeated Aku for the first time, and the world was restored to its former splendor, the Moons, no longer burdened by insanity, quickly regained their wealth and began the recruitment of Lunar Thugs. As stated above, after Corvo became President, he saw the benefit in employing bankers (because the Gearheads were not very good accountants) and they became part of Corvo's government.