Reapers is a type of angel, tasked with the duty of taking human souls to the Afterlife in Supernatural the CW TV show. Reapers are the children of Death, who has established the Natural Order with God, which shows that souls must move on, as being a ghost is somewhat unnatural.
A Reaper was the main antagonist in the season one episode Faith, where disgraced reverend's wife Sue Ann Le Grange was controlling a Reaper, against his will, to take human souls she perceived as immoral. However, the Reaper did seem to take sadistic delight in stalking, harassing, and killing people.
He took a young man's life in exchange for Dean's when Dean recovered from being electrocuted. The Reaper eventually was freed from his spell, and he realized what was happening, but he showed his sadistic side when he killed Sue Le Grange, and possibly took her to Hell.
The Reapers showed up again as the main antagonist in the season two episode In My Time of Dying, where after a demon attack Dean was almost dead in hospital, and in a coma. Sam was trying desperately to contact Dean's ghost, who was wandering the hospital. He eventually saw the true form of a Reaper: a swirling, wraith-like, misty entity, which was hovering over a young girl, about to claim her life.
Dean stopped the Reaper, and it appeared as a young woman named Tessa, first pretending she was deceased and delusional, but then Tessa revealed who she really was when Dean got suspicious of her acceptance of death. Tessa said she was just doing her job and she would move Dean onto Heaven or Hell, but she said evil ghosts are the ones who refused to be taken by a Reaper - thus Reapers are inadvertently responsible for dozens of human murders by ghosts in the show.
Tessa said she liked Dean, but urged him to hurry up and choose. Fortunately, John Winchester made a deal with the demon Azazel, who possessed Tessa and resurrected Dean, at the cost of John's life, as per the terms of the deal. Tessa may have taken John to Hell as the deal dictated.
Reapers do not appear again until season four and five when they are gathered to welcome their father, Death. Hundreds appear in streets, and Castiel says they appear in the prelude to mass disasters such as Pompeii's eruption.
The Reapers lure Castiel into an abandoned building Lucifer is using as a hideout, and soon after Lucifer frees Death from his coffin, and greets him.
The Reapers serve Death during the Apocalypse, claiming neither side (they are neutral in any conflict) and they go back to their own business when the Apocalypse is stopped.
In season six, Reapers make a bigger appearance. Dean calls to Death to help him free Sam's soul from Hell, to which an angry Tessa calls, and says why would he kill himself (he visited a surgeon) just to talk to Death. Tessa says Reapers do not call Death, he calls them. The Reaper Tessa and Dean get into an argument but then Death himself appears, thanks Tessa, and greets Dean.
Death gets Dean to be his position for a day and to teach him about nature. Dean does learn the hard way that messing with God's plan is bad.
When the brothers investigate Dick Roman's headquarters with Bobby Singer, Bobby tragically gets fatally shot by Dick when they flee. Dying in hospital, Bobby is visited in his spirit form by a Reaper, who follows him through his memories and persuades him to move on. This Reaper, unlike others, is calm, friendly, patient and understanding, but he does delight in showing Bobby how helpless he is and takes sadistic delight when Bobby finds out all his memories are gone. In the memory blackout, the Reaper persuades Bobby to come with him as his ticking clock echoes loudly as the blackout is complete.
In season eight, Reapers appear several times. One named Ajay has assumed the form of a young Middle Eastern man and is a taxi driver with access to Hell, and he takes Sam Winchester in, saying he, Ajay, was a rogue Reaper who deliberately took Bobby's soul to Hell rather than Heaven as was planned.
Crowley finds out about Ajay's dealing with Sam and kills the Reaper, with an angel blade, proving they are angels.
Another Reaper appears, this time in season nine, named Maurice, who was sent by Bartholomew to follow the Winchesters in order to find Castiel. However, they detected him and captured. The Winchesters then interrogated Maurice who revealed that he was trying to find Castiel and Naomi is dead and her protégé Bartholomew has taken over. Afterward, Maurice taunted Dean and provoked him into killing him which he did. Another reaper named April, who seduces Castiel, because she is very attractive, or at least her host is. She has possessed a human waitress named April, and she has also been sent by Bartholomew to kill Castiel. The fallen angel was attracted to her so twice they made love.
In the morning, April suddenly turned against him and she demanded Metatron's spells. April attacked and stabbed Castiel fatally, but Dean rushed in and killed in April.
Tessa later returned as she was recruited by Gadreel and later brainwashed by Metatron into suicide bombing. She was tracked down and captured by Dean before she could cause any damage. After being interrogated by the angels and explaining how depressed she was after she couldn't help the souls in the veil because of the fall, she killed herself using the first blade.
A reaper named Billie later appeared in Season 11 after the Darkness was released and Death was seemingly "killed" and paid Sam a visit. Upset that her boss was killed, she warned Sam that once he and Dean die it will be for good and no coming back.