For more information : Official website of Grey's Anatomy

Richard Webber

His real name is James Pickens Jr.
He is the head of Seattle Grace Hospital.
He loves Ellis Grey, Meredith's mother. He spends a lot of time in his hospital but his wife leaves him because they never see each other.

Miranda Bailey

Her real name is Chandra Wilson.
She is the head of the interns. She loves her job and she spends a lot of time seeing patients.
She wants to be the head resident.

Mark Sloan

His real name is Eric Dane.
He is a plastic surgeon. He wants to be the new head of Seattle Grace Hospital. He's coming on to Addison but she doesn't want to be with him.
He was Derek Shepherd's best friend.

Alex Karev

His real name is Justin Chambers.
He is a pretentious, haughty and beautiful man. He doesn't really have friends at the hospital.

Izzie Stevens

Her real name is Katherine Heigl.
She is a intern on the same team as Meredith, Cristina, George and Alex Karev. She is one of Meredith's roommates. She was married to Denny Duquette, a patient with a heart problem. But he died on their wedding day.

George O'Malley

His real name is T.R.Knight.
He is an intern at Seattle Grace Hospital. He is a roommate of Meredith and Izzie. He is married to Callie Torres.