Dr. Robert

He is a doctor that John Winchester knew. Dean visits him in season 6.

Background
He is a family friend of the Winchesters. He told Dean that he had stitched up John many times. He currently resides in an apartment above a Chinese place, and has lost his medical license. He also has an assistant who works with him.

So Dean comes to the doctor to temporary kill himself so he can find Death. When the two meet, the doctor gives Dean a hug and prepares Dean for the procedure. It works and Dean is dead for like 5 minutes and Dr. Robert manages to revive him.