Which actress played Dr. Addison Montgomery?

Kate Walsh played Dr. Addison Montgomery on Grey's Anatomy. Addison first appeared in the season-one finale as Derek Shepherd's estranged wife, arriving at Seattle Grace and immediately disrupting Derek's relationship with Meredith Grey.

Walsh was initially expected to appear only briefly, but audiences responded strongly to the character. Addison became a series regular in season two, where her expertise in obstetrics, gynecology, and neonatal surgery expanded the show's medical world beyond general surgery. Her complicated history with Derek and Mark Sloan became one of the series' defining early storylines.

Addison's popularity led to the spin-off Private Practice, which premiered in 2007 and followed her move to Los Angeles. Walsh remained the lead of that series for six seasons. A frequent mix-up is identifying Sandra Oh as Addison; Oh played Cristina Yang, while Katherine Heigl played Izzie Stevens. Walsh later returned to Grey's Anatomy for recurring appearances, reaffirming Addison's lasting place in the show's universe.