<P> Sara Ramirez acted as bisexual orthopedic surgeon Callie Torres, Eric Dane played womanizer plastic surgeon Mark Sloan, Kevin McKidd continued his portrayal of trauma surgeon Owen Hunt, while Patrick Dempsey acted as chief of neurosurgery Derek Shepherd . Meredith's half - sister and second - year surgical resident Lexie Grey was portrayed by Chyler Leigh . After having previously appeared in a multi-episode arc in a guest star capacity in the show's fifth season, Jessica Capshaw began receiving star billing in the season's premiere episode in the role of attending pediatric surgeon Arizona Robbins, love interest to Callie Torres . The ninth episode of the season marked the introduction of the new chief of cardiothoracic surgery Teddy Altman, portrayed by Kim Raver, whose mysterious romantic past with Owen Hunt develops into one of the season's main stories . Starting with the nineteenth episode of the season, Raver began receiving star billing . </P> <P> The sixth season introduces several new recurring characters who start to develop progressive and expansive storylines throughout the season . Mercy West surgical residents Reed Adamson, Charles Percy, April Kepner and Jackson Avery were portrayed by Nora Zehetner, Robert Baker, Sarah Drew and Jesse Williams, respectively . Jason George portrayed Miranda Bailey's love interest, anesthesiologist Ben Warren . Thatcher Grey (Jeff Perry) and Sloan Riley (Leven Rambin) have been part of the season's main story arcs, while numerous episodic characters have made guest appearances: Demi Lovato as Hayley, Sara Gilbert as Kim Allen, Marion Ross as Betty, Mandy Moore as Mary Portman, Ryan Devlin as Bill Portman, Nick Purcell as Doug, Michael O'Neill as Gary Clark, Danielle Panabaker as Kelsey, Adrienne Barbeau as Jodie Crawley, Héctor Elizondo as Mr. Torres, Amy Madigan as Dr. Wyatt, and Missi Pyle as Jasmine . Former series regular Kate Walsh returned to the series as a special guest star, portraying neonatal surgeon and obstetrician - gynecologist Addison Montgomery . </P> <Ul> <Li> Ellen Pompeo as Dr. Meredith Grey </Li> <Li> Sandra Oh as Dr. Cristina Yang </Li> <Li> Katherine Heigl as Dr. Izzie Stevens </Li> <Li> Justin Chambers as Dr. Alex Karev </Li> <Li> Chandra Wilson as Dr. Miranda Bailey </Li> <Li> James Pickens Jr. as Dr. Richard Webber </Li> <Li> Sara Ramirez as Dr. Callie Torres </Li> <Li> Eric Dane as Dr. Mark Sloan </Li> <Li> Chyler Leigh as Dr. Lexie Grey </Li> <Li> Kevin McKidd as Dr. Owen Hunt </Li> <Li> Jessica Capshaw as Dr. Arizona Robbins </Li> <Li> Kim Raver as Dr. Teddy Altman </Li> <Li> Patrick Dempsey as Dr. Derek Shepard </Li> </Ul> <Li> Ellen Pompeo as Dr. Meredith Grey </Li>

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