Early in Bonnie Hammer’s first stint running a cable network, she knew something was wrong. The SciFi channel was emerging as a destination for fans of the genre, largely on her strategy of reviving the mini-series.

But looking at the first day of shooting “Taken,” an alien abduction series with what then was the outrageous budget of $40 million, she knew the lead child actress was not strong enough. She pushed the show’s studio, Dreamworks, and its renowned producer, Steven Spielberg, for a different actress.

Her choice: the 10-year-old Dakota Fanning.

“Taken” vaulted the fledgling network to the No. 1 spot in cable ratings for two weeks, an early sign of Ms. Hammer’s astute programming instincts and of a quality her mentor, Barry Diller, called “a steely resolve.”

A decade later, Ms. Hammer has ridden that resolve and those instincts to a position of enormous influence and financial power in cable television. If cable is king, Ms. Hammer, chairwoman of NBCUniversal Cable Entertainment, is cable’s queen and, since the departure of Judy McGrath from Viacom last May, possibly its most important executive.