Robert Sean Leonard will reprise his role as Dr. Roger Kadar in the upcoming fourth season of Falling Skies. Although fans have noticed that he was almost unrecognizable, TV Line has confirmed that the former House actor will appear in atleast one episode of season 4.
Kadar formerly worked at the University of South Carolina, teaching nuclear physics. Sometime after the invasion, Arthur Manchester found Dr. Kadar and struck a deal with him to run Charleston's power grid. (source)
The 10-episode Season 4 will premiere in summer 2014.