Dr. Miranda Bailey
Miranda Bailey, a graduate of Wellesley College, is a resident surgeon who was also previously in charge of the five interns (now second-year surgical residents). Her colleagues refer to her as "The Nazi" because of her tough personality and blunt attitude. Although often harsh with her interns, she has been shown to provide both support and advice when they need it; some might say she practices "tough love." She married Tucker Jones c.1995.
Her son, William George Bailey Jones, was born during a bomb scare at Seattle Grace while her husband was in surgery with Dr. Derek Shepherd, having crashed his car on the way to the hospital (It's The End Of The World/As We Know It, a two-part episode). George O'Malley helped her through labor, and she thanked him by naming her son William George Bailey Jones (although he is nicknamed "Tuck" for his father).
Dr. Bailey is known for being a compassionate doctor; Bailey stayed by Cristina during her pregnancy scare and her initial recovery and also held Izzie's hand when Izzie was giving bone marrow for her daughter. She cares about her patients and is a committed surgeon.
Through the rest of season 2 into season 3, Bailey was seen adjusting to becoming a parent and reconciling this with her desire to continue her career as a surgeon. Her professional confidence was shaken when Izzie Stevens cut Denny Duquette's LVAD wire and Denny subsequently died after his heart transplant; Bailey felt that she wasn't in control of her interns, and that the incident was ultimately her fault. She was criticised for the events at a Morbidity and Mortality conference in Oh, The Guilt, with one colleague questioning outright her competence at juggling career and motherhood. While her confidence has been somewhat restored since then, she still feels bad about not spending enough time with her son, once making a late-night call to sing "God Bless the Child" to him.
Disillusioned by how little she can help patients as a surgeon, Bailey decided to open a free clinic at Seattle Grace in the middle of season 3. She faced initial difficulties getting support from the attendings, but after talking with the Chief, managed to get their agreement to work there. The Denny Duquette Memorial Clinic has since opened, paid for using part of the $8.7 million bequeathed to Izzie by Denny Duquette, and Bailey is satisfied that the clinic will change people's lives for the better. She competed for the post of Chief Resident, but in the final episode of Season Three, she found out she lost to Callie Torres. Dr. Richard Webber indicated that she could become Chief of Surgery in a few years' time.
In season four, Miranda decided to be Callie's "number two," as Torres was lacking of competence as Chief Resident. The Chief saw Bailey pick up the slack, and delegate exceptionally well, and eventually realized that Miranda was covering for Callie. He terminated Torres from the position, and told Bailey that he made a mistake in not giving her the job in the first place. He also apologized for taking Dr. Bailey for granted. At this Miranda broke down in tears hugged the Chief. This is an example of the emotional baggage the "Nazi" carries, and shows one of her very rare emotional moments. During season four Miranda helped save the life of a white supremacist paramedic despite his racist treatment of her. When closing his stomach after the surgery, she comments to George that the incision will need to be aligned better, thus ruining the paramedic's large swastika tattoo on his stomach. During the surgery she declared that she "will not be called the Nazi ever again." Following severe injuries to her son in late season four and several arguments over the state of their marriage, Doctor Bailey and her husband separated because her husband believed that she placed her job at the hospital before her family and that it led to Tucker's injuries. In the finale she turned control of the clinic over to Dr. Izzie Stevens citing that she had earned it.
In season 5, Christina confessed to Bailey and Alex Karev that Izzie had skin cancer, was refusing treatment and begged them to help. Bailey, like all the other residents and interns, was devastated to learn of this and set about helping Izzie recover.
Source: Wikipedia.org