Casting is the great unsung art of movies and TV. Get it right on the nose, and all the credit tends to go to the actor who was such a perfect fit for the role he or she was hired to embody. Get it wrong, really, really wrong, and your tiny obituary in Variety may be built around the line, "Mr. Crabtree was perhaps most legendary among his colleagues for the fateful lunch at which, distracted by the collapse of his marriage and having been up for three days on a cocaine bender, he offhandedly remarked to Oliver Stone that he thought that Colin Farrell would make a perfectly credible Alexander the Great."

Of course, some roles offer more opportunity for public humiliation than others. Say that you have a little corner office at HBO and have been assigned the task of finding an actress to play a nomadic mystery woman who shows up in a small Louisiana town, begins to quietly make her presence felt, reveals that she has supernatural gifts, and finally emerges as a full-blown force of nature: a Dionysian "maenad" who has literally willed herself to achieve immortality, and whose sexual energy is so potent that it fogs the minds of those around her, reducing the local populace to a slavering, mindless rolling orgy devoted to helping her carry out her plans for a human sacrifice. That's a casting job to make a man shudder, and maybe experience nightmares in which he learns that the only performer available for the role is Meg Ryan. But whoever had the job of finding someone to play Maryann Forester on True Blood must have reacted to the news that Michelle Forbes was on board by doing a festive little dance and putting the loaded pistol back in his desk drawer.

An actress playing a character whom other people respond to with Manson-family levels of adoration has a terrific advantage if the camera itself worships her. Forbes had that much of the job locked up before she first reported to the set. She has the kind of face that jumps out at you from the third row of a crowd scene. One's attention first tends to focus on the eyes, which are very dark and unfailingly intense, and her strong, arched eyebrows, which automatically make her look both imperious and intimidatingly smart. (She can seem so to an unearthly degree, which probably helped her land one of her first attention-getting roles, as the Bajoran ensign Ro Loren on Star Trek: The Next Generation.)

A less committed performer could have coasted on those eyebrows alone, but Forbes likes to keep you guessing, and one of her trademark maneuvers in the past has been to use the softening possibilities of her mouth and chin to suggest a degree of insecurity that you might not have suspected in someone who seems so assured. For a couple of seasons she played the coroner on Homicide: Life on the Street, where she fell into an affair with a hard-drinking, self-destructive police detective played by Reed Diamond. Her character was a hardass about the integrity of her job, but there was a memorable moment when Diamond's partner pestered her about what the two of them were getting up to. "Shut uuuup!" she said, with a big smile, and the effect was sort of like seeing the sixteen-year-old girl who might conceivably still be somewhere inside Madeleine Albright. At moments like this, when a toothy grin breaks or a trace of self-doubt roils the placid surface of Forbes's face, it becomes very difficult to concentrate on the drama at hand instead of writing a better one in the quiet of your imagination. I find it helps if I stab myself repeatedly in the thigh with a pencil.