The chief of surgery at Seattle Grace Hospital. He strives to balance both the medicinal and financial sides of running such an important institution.

Richard often refers to the financial implications of things, such as Derek punching out Mark (and risking his "$2 million-per-year hand"), or why he cannot prevent the nurses union from striking.

In Season One, he had Derek operate on a tumor that was pressing on his optic nerve, emphasizing that the surgery be downplayed so his position as chief surgeon wouldn't be jeopardized. Dr. Webber made a full and speedy recovery and retained his post.

Considered a mentor to both Dr. Burke and Dr. Shepherd, two of his hospital's elite surgeons and both of whom aspire to succeed him as chief of surgery. Richard is also a close friend of Dr. Ellis Grey, mother of Meredith. Recently it was revealed that he and the elder Grey may have had an affair.

Little is known about Dr. Mark Sloan, the newest full-time character on Grey's Anatomy, but that doesn't mean he isn't noteworthy. In fact, his being shrouded in mystery for much of the series only increases his appeal.

That, and he's McSteamy. He's the man, revealed in Season 2, who was the catalyst in Derek and Addison's divorce. It was upon walking in on Mark and Addison in bed together that Derek fled New York for Seattle.

There, the neurosurgeon began a romance with an intern named Meredith, and the rest is history. Well, sort of.

When Addison eventually came out to Seattle, Derek took her back and they tried to reconcile. So when Dr. Sloan appeared one day, he was not well received... by Derek's fist. He sutured his own face after being cut.

Mark's purpose was to take Addison back to New York, as he is very much in love with her. A plastic surgeon, he ended up assisting on a rare operation during his brief stay and giving career advice to Alex.

Despite his best efforts, though, Addison did not follow Mark back to New York. But in the second episode of the third season, he appeared wearing nothing but a towel in Addison's hotel room, after receiving a transcontinental booty call. Mrs. Dr. Shepherd had just learned of her husband's affair with Meredith and embarked on a serious bender -- one that ended with Mark back in the Emerald City.

It was the most talked about moment of the season to date, but we're sure many more will come from Mark, who's sticking around and determined not to let Addison slip through his fingers a third time.

Derek is a renowned brain surgeon who we are led to believe moved to Seattle from New York a little bit before the series debuted. He and intern Meredith Grey met and slept together during the pilot, with their romance blossoming soon after.

Derek is married to Dr. Addison Montgomery Shepherd, who he left in New York after finding her in bed with his best friend Mark, a plastic surgeon. Addison joining the staff at Seattle Grace during Season One resulted in constant conflict for Derek as he struggles to repair his marriage and deal with his feelings for Ms. Grey.

Dr. Shepherd was nicknamed "McDreamy" by the female interns at Seattle Grace. The man has some amazing hair. He and Dr. Preston Burke are among the hospital's top surgeons and there has been occasional friction other which one the chief, Dr. Richard Webber, will name as his successor.

The arrogant, handsome intern who is both repulsive and irresistible to Izzie. The two have an on-again, off-again relationship that is currently off, largely due to Alex getting caught sleeping with a nurse - in an attempt to regain confidence after "performance anxiety" problems with Izzie.

A former wrestler at the University of Iowa, he often tries to act more tough and aloof than he actually is. He and George O'Malley have never gotten along, partly due to general personality clashes and also because Alex indirectly gave him syphilis (in Season One, George dated and slept with a nurse that Alex shagged).

After he and a visiting surgeon (Mark, the former best friend of Derek and lover of Addison) discussed his career prospects, Alex expressed interest in becoming a plastic surgeon.

She's abrasive, afraid of commitment, doesn't "do" emotion and is extremely competitive about getting the "cool" surgeries. She is of Korean descent and is a native of Beverly Hills, Calif. Cristina graduated from the Stanford University School of Medicine and maintains a love-hate relationship with her mother.

Despite being his polar opposite in many respects, she began dating Dr. Preston Burke during Season One. She became pregnant, only to have him break off their relationship for professional reasons. Cristina planned to have an abortion without telling Burke, but changed her mind after talking to a pregnant patient. She later collapsed during a surgery with Burke, and was diagnosed with an ectopic pregnancy, which was surgically terminated.

Despite his emotional and physical trauma, she and Burke got back together soon after. The evolution of Cristina's relationship with Dr. Burke is a focal point of Grey's Anatomy. She only told Burke she loved him while he was asleep, and didn't give up her apartment for months after moving in with him. Cristina is particularly close to Meredith, although she is also friends with George and Izzie.

A statuesque blonde, Isobel "Izzie" Stevens put herself through medical school by modeling. Underwear. Wow.

When this fact is publicized by Dr. Alex Karev, who pins pictures of her up in the locker room, Izzie flys off the handle. She later warms up to Alex, however, and dates him briefly before catching him sleeping with a nurse and breaking it off.

At first, Izzie butted heads with Meredith over the latter's relationship with Dr. Shepherd. Izzie initially believed it was a plot for Dr. Grey to get ahead of her fellow interns, but the two have become good friends. They live in the same house, one that was also inhabited by George until the most recent episode.

When meeting a pregnant teenage girl from her hometown (outside Seattle), Izzie revealed that she, too, had a daughter at 16. Her daughter, who is now 12, was adopted and now lives in Santa Barbara, Calif. Izzie has shown an interest in surgery involving infants and extremely young children, the specialty of Dr. Addison Shepherd.

Fell in love with everyone's favorite patient, Denny, before he died from heart failure. In her illegal attempt to save him, Izzie risked her entire medical career.

The interns' boss. Also known, affectionately, as the Nazi. She's bad-ass.

From the moment she first met the interns, she made her presence known by telling them not to bother sucking up, because she already hates them, "and that is not going to change." Not surprisingly, there has been no sucking up -- or talking back -- to Miranda ever since.

Miranda's softer side has made more frequent appearances of late, however, as she became pregnant and gave birth to her first child. At first, she kept a low profile regarding the pregnancy, but her cover was blown after she turned down an elite fellowship opportunity and Dr. Webber became convinced she was quitting.

Dr. Bailey reached an emotional breaking point when her husband was hospitalized with severe head trauma, sustained in a car wreck on his way to the hospital. George helped her stay calm through the birthing process, while Derek was able to repair the damage to her husband's brain.

All during a CODE BLACK!

Introduced near the end of Season Two as the love interest of George, this orthopedic surgeon is not afraid to ruffle the interns' feathers.

Dr. Calliope "Callie" Torres first appeared in episode the "What Have I Done to Deserve This?" She met George when treating him for a dislocated shoulder, which he suffered falling down the stairs... fleeing Meredith.

While she appears to be a strong woman on the surface, Callie clearly has her insecurities. She grew defensive after being criticized by Izzie for not washing her hands after using the bathroom, and actually lives in the hospital basement, as discerned by George in "The Name of The Game."

Yet she clearly adores Dr. O'Malley, which dawned on Izzie eventually, as the blonde beauty famously noted, "Oh my god... George is her McDreamy!"

In the episode "17 Seconds," Callie proclaims her love for George, later revealing that this was the first time she said that to a man. While he didn't say it back, he admitted that he wanted to give himself the chance to. Callie replied that she "hates that she's so into" George.

But she is, just the same. We look forward to seeing more from this feisty doc in Season Three!

One of the most compelling characters on the show. When viewers were first introduced to Mrs. McDreamy, she was the villain, arriving in the Emerald City just in time to ruin Meredith's relationship with her husband. It turns out that Derek left New York for Seattle after catching her in bed with Mark, a plastic surgeon and his best friend -- a fact he conveniently withheld from Meredith.

While she gave Derek the chance to sign divorce papers and end things between them for good, he declined. They have slowly begun to patch things up, although much guilt and resentment remains. The reappearance of Mark, who tried to lure her back to New York, did not help matters. Addison also hates living in Derek's trailer, and the fact that he adopted Meredith's dog.

Addison specializes in surgery involving extremely young children, including those still in the womb. She has become a mentor to Izzie, and a commanding presence throughout the traditionally male-dominated hospital.

A heart transplant patient who falls in love with surgical intern, Dr. Izzie Stevens. Izzie sacrificed her career by cutting his LVAD wire to worsen his condition so that he would receive a heart from a patient whose intended recipient was ahead of Denny on the list by seventeen seconds. He proposed to Dr. Stevens shortly before dying of a stroke in the final episode of season two. He left Izzie with a check for $8.7 million in episode 3.04, What I Am, which Izzie finally deposited in Season Three's Episode "Six Days" after an intense moral dilemma. Izzie used the funds to help Dr. Bailey create the Denny Duquette Memorial Clinic. Denny once again returned in "Some Kind Of Miracle" when Meredith had her brush with death. Jeffery Dean Morgan hosted the third season re-cap special, "Every Moment Counts".

The owner of the Emerald City Bar - across from the hospital - where the doctors often go for a drink, and is also where Derek and Meredith met. Derek and Burke performed a stand-still surgery to clip an aneurysm in Joe's brain. Joe and his boyfriend Walter (Jack Yang) also attended the Thanksgiving Izzie hosted at Meredith's house, and went on a camping trip with Drs. Shepherd, Burke, Webber, Karev and O'Malley. During this trip, Joe revealed during a discussion with the Chief that although he and Walter had been "on-and-off" for about ten years, they were now committed and considering the possibility of children. They are one of two couples being considered as adoptive parents for a young mother's twins.

Lexie is the daughter of Thatcher and the late Susan Grey, and the younger half-sister of Meredith Grey. She also has a younger sister, Molly Grey Thompson. She is a graduate of Harvard Medical School.

Lexie is a new intern at Seattle Grace Hospital. She was introduced in the penultimate episode of the third season as the woman Derek Shepherd met at Emerald City Bar.

In the third season finale, Derek confesses to Meredith he met another woman (though he doesn't specify who) and when she asks if she should be worried, he confirms her fears. Lexie would make her first appearance in Seattle Grace when she introduced herself to George O'Malley, who realized her connection to Meredith.