Eliah was a penitent angel whom Castiel contacted.
Biography
He told Castiel how penitent angels were living humbly among humans but this angered Bartholomew. Eliah was paying respects to his friend Rebecca, who led the penitents. Eliah left in a hurry, wanting to avoid Bartholomew's angels, who were on the hunt for remaining penitent angels. Sure enough, shortly after Eliah fled, angels from Bartholomew's faction arrived and captured Castiel.
Eliah was later captured by Bartholomew's angels. Although initially tortured for information by Bartholomew himself, Eliah's true purpose was used as a test devised by Bartholomew for Castiel to prove his dedication. After Castiel refused to agree, Bartholomew stabbed Eliah in the stomach, killing the penitent.