Most of you are familiar with the recent Battlestar Galactica show, which as you know was a fictionalized retelling of an earlier pair of documentaries produced in the late seventies and early eighties. The first documentary told the story of the survivors of the Twelve Colonies and their search for the fabled "lost" thirteenth colony, Earth. The second documentary examined their arrival on Earth and their attempts to keep Earth safe from the Cylons - the same robotic forces which had destroyed the Twelve Colonies.
What the Colonials didn't know was that the Cylons were already on Earth. Apparently their hostility was reserved for the humans of the Twelve Colonies. Earth humanity was considered harmless, blameless, or simply too ignorant to merit destruction. So, while the crew of the Galactica struggled to keep Earth safe from the Cylons, the Cylons worked quietly in the background to save Earth humanity from itself.
They set up front companies to disguise their influence, and either found or created human(-seeming) proxies to be their spokespeople. Probably the best known of these was Knight Industries, which developed a very effective working partnership between a human and a Cylon under its FLAG program.
No, I'm not making this up. The FLAG program had its own documentary, though it was more of a PR exercise than the ones devoted to the Battlestar and its crew. Let me find a sample...
Here. Look at this, and tell me it's not a Cylon: