Dr. Sidney Miller is an evolutionary biologist. Who works with Dr. Ellis Watts at New York University. During a research dig in New Mexico a few years back he found remains of a Visitors. Sidney named the lizard skeleton with razor-sharp teeth Alpha and kept it hidden from the rest of the world.
Sidney was the first to reach the truth of the Red Sky phenomena, but the Visitors thought it was Dr. Ellis Watts who knew the truth because Sidney accessed his computer. ("Red Rain")
He is an important asset for Erica Evans, to find out if the Vs experimented on her when she was pregnant due to her story of how she had abnormally high levels of Phosphorus, the large amount commonly and mainly found on the V homeworld. He analyzed Tyler Evans DNA to discover that there are huge chunks missing, as if waiting for an input. ("Serpent's Tooth")
In investigating the DNA of both Alpha and Sarita Malik, Sidney discovers that the Visitors have evolved more quickly that normally possible, with Sarita Malik's DNA much more complex than Alpha's. This leads him to conclude that the Visitors are using genetic engineering to advance their species. ("Laid Bare")
Sidney joins in the Fifth Column raid on a lab to steal the DNA virus, and then prepares the samples to be shipped to the various operatives to infect the live-aboards. ("Uneasy Lies the Head")
he then helped the rest of the team figure out the concord structures were landing pads he then disguise himself as a construction worker for a concordia structure and was helped to get into the blue energy by evan and fifth columnist guard and when he saw Ryan Nichols after sabotaging the blue energy reactor he attempted to do something bad but was stopped he then showed the team that the 538 visitor ships were already here ("Devil in a Blue Dress")