Employing iconic black-paper silhouettes, Kara Walker — who was named one of Time's "100 Most Influential People" in 2007 — sparks a tense dialogue between artist and viewer with her installations and animated films. At the Hammer Museum, her scathing retelling of American history through images of sexual violence, racial stereotypes, and antebellum mores finally receives the retrospective treatment. Her room-sized narrative installation Darkytown Rebellion engulfs viewers with a colored-light projection layered over a grotesque Southern parade; in the early paper silhouette Cut, a woman's ecstasy can easily be confused with her self-inflicted pain. As discomforting as Walker's imagery may be, her tenacious instincts for artistic precision, provocation, and humor mobilize in equal measure.