Heigl played intern Izzie Stevens, in a continuous struggle to be looked upon as a doctor, not the model she used to be. Justin Chambers acted as Alex Karev, who begins to develop an emotional side of his personality, after being introduced as arrogant and selfish. T. R. Knight played the role of intern George O'Malley, whose insecurity and lack of self-confidence evolve due to his unshared feelings for Meredith Grey. Chandra Wilson portrayed surgical resident and brilliant general surgeon Miranda Bailey, the mentor of the five interns, whose rudeness and cold attitude earns her the nickname "The Nazi." James Pickens, Jr. portrayed Seattle Grace Hospital's Chief of Surgery, Richard Webber, whose relationship with Meredith Grey's mother, which occurred 21 years ago, threatens to ruin his marriage. Isaiah Washington played the role of attending physician and cardiothoracic surgeon Preston Burke, who learns that Cristina, with whom he had a sexual relationship, is pregnant with his child. Patrick Dempsey portrayed attending neurosurgeon Derek Shepherd, whose relationship with intern Meredith Grey has been the focal point of the series since its inception. Although originally conceived as a guest-star with a 5-episode story arc, Kate Walsh decided to extend her contract following positive reviews from critics and fans, resulting in her getting promoted to series-regular status. Being the first addition to the original cast from the first season, Walsh began receiving star-billing in the seventh episode of the season, portraying obstetrician-gynaecologist and world-class neonatal surgeon Addison Montgomery Shepherd, who comes in Seattle seeking reconciliation with her estranged husband, Derek Shepherd. Numerous supporting characters have been given expansive and recurring appearances in the progressive storyline. Sara Ramirez appeared in a 9-episode arc in the season, portraying orthopedic surgical resident Callie Torres, introduced and developed as a love-interest for the character of George O'Malley. Steven W. Bailey is introduced in the recurring role of Joe, the Bartender, often being portrayed as a confidant of the surgeons of Seattle Grace Hospital. Chris O'Donnell portrayed veterinary physician Finn Dandridge, who became a love-interest for Meredith Grey. Renowned surgeon Ellis Grey, Meredith's mother, who is suffering from Alzheimer's disease, continues her recurring role from the first season, being portrayed by Kate Burton. Brooke Smith portrayed Erica Hahn, a cardiothoracic surgeon at Seattle Presbyterian Hospital, who is revealed to have been a rival of Preston Burke ever since they attended medical school together. Jeffrey Dean Morgan appears in 6