Meredith Grey:

Daughter of the famous Ellis Grey, whom she visits daily in a special care facility. Secretely dating/sleeping with Dr. Derek Shepherd.

Isobel "Izzie" Stevens:

Relied on modeling to pay her way through Medical School. Has a somewhat outgoing personality and a big heart.

Together: Their two strongly differing personalities make for a very interesting, but loving relationship. They live together, along with George in Meredith's mother's old house.

more later...