Karen Nadler was a main character in the first, second and third season. Karen was a scout for the 2nd Massachusetts Militia Regiment. She was romantically involved with Hal Mason in Season 1. Captured and harnessed by Skitters, she turned her back on humanity and began willingly serving the Espheni. Becoming a agent for the Overlord overseeing the eastern United States, she helped him hunt down a rebellion among the Skitters which led her to return to the 2nd Mass. Her efforts were in vain however, and the 2nd Mass destroyed a Espheni canon and killed her master. She served as the main antagonist of Season 3.
Karen was appointed by her masters to take his place, overseeing all military operations in eastern North America, including destroying the humans, the rebel Skitters, and the Overlords' interplanetary enemy, the Volm.
Karen was eventually killed by Maggie after the destruction of the Mothership in Boston, being shot multiple times after she tries to wave a white flag and work with the 2nd Mass.
