Rift Guardians are the special Unique monsters who appear when enough enemies have been killed in a Nephalem Rift to fill the progress bar to 100%. The Rift Guardian must be killed to finish the Rift and earn a big reward from the Guardian's drop.

Greater Rift Guardians are the same monsters as normal Rift Guardians, though they are powered up with greater abilities in higher level Greater Rifts.