Dr. Preston Burke
Preston Burke is the former chief cardiothoracic surgeon at Seattle Grace Hospital. He completed his pre-medical studies at Tulane University, and went on to graduate first in his class from Johns Hopkins Medical School. While in college, he met Erica Hahn, who graduated in second place after him, beginning a rivalry between them. He was once the interim chief of surgery while Dr. Webber was healing from his brain surgery. He began a relationship with intern Cristina Yang but broke it off because he feared it would ruin both of their reputations. Her miscarriage brought them back together. He and Cristina lived together in his perfectly-kept apartment.
In the second season finale he was shot, which affected his control of his right-hand. His temporary fix to this possibly long-term problem was to work together with Cristina during every one of his surgeries so that she could take over in case he might have trouble with his hand. The arrangement fell apart after Cristina, reacting to growing stress after George caught onto their secret, went to the Chief and confessed everything. Initially, he was engaged in a cold war with Cristina, where neither of them spoke (neither would "say Uncle") but after she broke the silence, he proposed to her and she accepted his proposal. Before their secret was revealed, Burke was to become the next Chief of Surgery, but he had to compete with his fellow attendings for the position. He has since recovered from the injury, after Dr. Derek Shepherd operated on him.
For the remainder of the season, Preston and Cristina prepared for the wedding and experienced normal stresses that result from such a process; including with events such as meeting each other's parents.
However, in the finale of season three, on the day of their wedding, Burke told Cristina that he no longer wished to make her do anything against her will, and realized he was trying to make Cristina the woman he wanted her to be, and not accept her as the woman she is. Cristina said she "thought this was what she wanted." He wanted her to say she knew it was what she wanted, so he left her in the chapel. Cristina then returned to their apartment and discovered Burke had left, taking with him the things that meant something to only him (his trumpet, his Eugene Foote collection, his grandmother's picture, and his lucky scrub cap), leaving Cristina devastated.
In season 4 of Grey's Anatomy, Preston's long-time rival and love-to-hate medic Dr. Erica Hahn replaced him as the head of cardiothoracic surgery. Having such, she has a huge respect for Burke although she would never admit it to his face. She was even appropriately nicknamed The New Burke and Dr. McHardcore. Hahn dislikes Christina Yang because of her relationship with Dr. Burke. During his employment at a new hospital, he is made the recipient of 2008's Harper Avery, a highly prestigious medical award.
Source: Wikipedia.org