Reapers

There are two types of reapers that we see in the show.  The first one comes from the episode "Faith" and they are more commonly known as a psychopomp.  These types of reapers are usually a spirit or entity whose responsibility it is to escort newly-deceased souls to the afterlife.

The second type of reaper we see comes from the episode "In my Time of Dying".  This reapers appears before Dean as a young woman named Tessa because he rejected her true form.  She is usually considered the more common of the two reapers because she resembles "Death" in many ways.