Dr. Calvin Horn is the main antagonist of the first half of season 2 of Revolution. He was a member of the Patriots. In a conversation with Rachel, he described himself as the President's Chief Science Adviser.
When Horn was a boy he watched helplessly as his mother died of an unnamed illness. His father was deeply (bordering fanaticly) religious and tried to pray the illness away, but to no avail. Horn did not believe in miracles and offered several times to get medicine from his friend's father, but his father refused every time. One day Horn secretly got the medicine and gave it to his mother. However his mother died anyway and upon finding out what his son had done, his father blamed him for her death because he gave her the medicine. When Horn grew up he became a scientist working for the D.O.D., helping with their alternative energies project. While working there he meet Rachel Matheson and worked with Ben Matheson's team on the project, but he was only as a very minor figure in the events.
After The Blackout he was on the first boat leaving D.C. with (the future) President Jack Davis and Randall Flynn heading for Cuba. With the others he moved to a base in the Gulf of Mexico. Fifteen years later, after the Patriots began returning to America, during this time he rose to the position of the President's Chief Scientific Adviser and apparantly began practicing human experimentation, developing a terrifying reputation for himself. It was here he examined the burned bodies sent back by Truman. At some point Horn learned he had a fatal tumour in his brain, lacking the medical technology to treat it, he initially gave up hope, only for the examination of the bodies to provide him with a possible answer. When he learned the bodies came from Willoughby and that Rachel was in Willoughby he ordered everything packed up, saying that they were heading to Willoughby.
A couple of days later he arrived in Willoughby, Texas and met with Rachel to discuss the Nanites. He knew they must have been reprogrammed to save Arron and kill Truman's soldiers and he figured that it was Rachel that reprogrammed them. When he found out it was not her, he met with Dr. Porter and asked him to tell him about Aaron. Forced by Horn, Gene planned to hand over Aaron to Horn to save his family, but Miles saw through their plan and snuck Aaron and Cynthia out of town. Once he found out that Aaron escaped Horn ordered Truman to send all The Patriots out and find Aaron, claiming if he could harness the nanites power the Patriots could take back America in a matter of weeks; he also warned Gene to find Aaron before he found Rachel or else he would kill her.
The Patriots eventually found Aaron and Cynthia and forcibly brought them back to their secret headquarters. He initially told Aaron he was not going to hurt him, he just wanted to help him better understand the Nanotech. He proceeded to experiment on Aaron by cutting him and watching how he miraculously healed every time. His interest growing he told Aaron that he wanted to see if Aaron could heal someone else. He then had his men bring in Cynthia and proceeded to stab her in the side. By doing so he inevertantly caused Aaron to knock everyone out and escape.
Upon awaking he noticed Aaron had escaped, he ordered him tracked down and brought back. Horn followed Aaron's trail through The Patriots' secret tunnel and into the woods outside of Willoughby. He ordered his men to fan out and search, but his search was impeded by Miles, Rachel, Charlie, and Monroe. With the fog thickening, Martin Shaw told him he needed to fall back. With his condition worsening he ignored Shaw and continued the search. He soon received word that Aaron was at the abandoned High School, and ordered the Patriots head in that direction.
When they arrived they were met with resistance from the four who were helping Aaron and Cynthia escape. Monroe, Charlie, Rachel, and Miles held them off long enough, but they were all eventually cornered. While Rachel tried to protect an unconscious Miles in the library, Monroe and Charlie were busy fighting them off in the gym, and Aaron and Cynthia were confronted by Horn himself. Holding them at gunpoint Horn ordered Aaron to remove the tumor from his brain, Arron tried to explain he didn't have that sort of control over the nanites, but Horn wasn't listening, when Arron didn't save him, he killed Cynthia and prepared to kill Aaron. In that momment of emotional trauma Aaron managed to call the Nanites to him, who appeared and asked for his orders. He told them to kill Horn and all the Patriots attacking saving Miles, Rachel, Charlie, and Monroe in the process. As such they caused Horn to burn to death.
After his Death, Horns apperance and mannarisms, were duplicated by the Nanites in a dream state they placed Aaron into, to try and force him to fix there code. Replicating Horn, cause he was what Aaron fear the most.