Doc

Doc was the dog of Meredith Grey, Addison Montgomery and Derek Shepherd.

Personal life
Doc was adopted by Meredith and came to live at her house. Her roommates however (particularily George) didn't like him around the house so George delivered Meredith an ultimatum, him or the dog. Eventually Meredith decided to give the dog to Addison and Derek.

Doc had a vet named Finn and was revealed to have cancer, as a result, Finn put him down. When Meredith drowned in Elliot Bay, in the afterlife, she met a completely healthy, Doc.