Creation:
The Grim Reaper was originally created in 1508 with the first ever of his species, Orano Ivanovitch. He was created by the angels and sent to Purgatory to eventually be a being of leadership within the realm. Like the angels looked after earth, and hell had Lucifer, Purgatory needed its own divine being. The Grim Reaper was created to transport souls from earth to their respective afterlives, whether that be heaven or hell and while originally, the idea was to have one, being Orano, that would work as such for all of eternity- that is not what happened. It ended up as one serving, with or without a partner to help, and eventually when they decided it was time to retire, another would take their place- usually a relative of the former. The length between how long one serves versus another varied dramatically, one taking over the mantle for nearly 400 years and another only having it for a little over twenty.
A new Reaper:
The transferring of the job from one Reaper to the next is where things get a bit complicated. Usually a person begins the training process in their mid to late teens, and this consists mostly of learning about position and the responsibilities it entails- a lot of this is focused on the political side of the job rather than the other sides. In this stage of learning, they're meant to slowly start putting their name out there more and get acquainted with the people they'll be working with- and even choose their own new members to take on.
This stage usually lasts one to two years, depending on how old they are and how committed they've been to their tasks. The former grim Reaper will slowly start to lose their powers and the upcoming will slowly gain them- most times without even realizing it's happening. As the new Grim Reaper slowly grows more powerful, they will start taking on more responsibilities- accompanying their mentor to reap souls and show them the way to escort ones to the afterlife. While this is the most important part of the job, and the reason they were created, this part is often overlooked by others.
In these last few stages they are almost a fully fledged Grim Reaper, but won't qualify as one until the former retires. During the process where one Reaper is taking over for another is a very unstable time for the Grim Reaper Mantle- where there is technically no full power Reaper for a few years. This seems like a flaw in the system, but remember that the Grim Reaper position was originally created for one person and not to be changed periodically.
Abilities:
As we know, the Grim Reaper is a powerful entity within Purgatory, but how far does that power really go? Especially in comparison to other species. The Grim Reaper is a being created specifically to help reap souls from their former bodies and take them to their afterlife, being heaven or hell- so, as you can probably imagine, their powers have a lot to do with that.
Scythe Summoning: Grim Reapers have the ability to summon a scythe- seemingly out of thin air to those who aren't aware how they work. Contrary to popular belief, they are not creating it- the scythe is just an extension of themselves, they are just bringing that extension to life. A reaper's scythe is probably one of their most important aspects to the job- they quite literally need it. The Grim Reaper's scythe itself is one of the most powerful weapons one could yield- and one that has reaped souls can break just about any magic object.
Touch/control Spirits: Unlike all other living things, Grim Reapers have the ability to touch spirits/ghosts (and see them!), this mostly from the fact that Grim Reaper's are not really 'living' or 'dead', but at an inbetween state. Controlling ghosts, however, is a skill that does not come to all grim Reapers. While they all have the ability, it can be difficult and few have actually mastered it.
Death touch: Grim Reaper's can kill a living thing by simply touching it- this can be a difficult power to control to new reapers, and probably the most powerful ability they possess. This applies to ALL living things, from grass to adult humans. Having a scythe helps them channel this ability, which is why it's so important for them to be able to summon their scythes.
Grim Reaper's also possess a few minor abilities, such as: being able to tell when someone is going to die (sometimes even how), releasing a 'black smoke' that is often referred to as 'death's cloud' from their scythes- this usually causes no physical harm to others, is more to conceal them. They also have a connection to Purgatory that allows them to have something of a 'sixth sense' when it comes to danger or other things that could be going wrong. With this connection to Purgatory, they have the ability to control what leaves and enters Purgatory, and can open a portal to and fro wherever they please- as opposed to all other species, which do not have that ability. Because Grim Reapers are technically the only creatures that should be able to freely travel between the two realms. They can also freely open the gates of heaven and hell (obviously) but they are not supposed to enter either. They heal much faster than a regular human would, and possess slightly elevated senses.
While their abilities are stronger in Purgatory than Earth, there is not much of a difference between what they can do; However, on Earth, a Reaper becomes invisible to the human eye when their scythes are summoned.
Death:
As you can imagine, killing a reaper is no easy task- because they were not designed to die. Actually, one of the only ways to kill a reaper is by using its own scythe against them. Because of this, Grim Reapers are actually immune to a lot of different witch spells and poisons- but not all. And the ones that do work against them would need a higher dosage.
They are not invisible though, and can get hurt like any other species- it just affects their bodies a little differently. Like, if they were to get attached and get severely injured- their hearts wouldn't stop beating, but their bodies would go into an almost hibernation-like state to heal. Like mentioned prior, their bodies heal much faster than that of an average human- so what may take a human several months to recover from, may only take them a week or two.
Reaper v. Grim Reaper?
While they sound like they could be the same, keep in mind that these two are different- Reapers are like a subcategory of Grim Reapers. There will only ever be one or two Grim Reapers, this is a very special and powerful position- Reapers, however, are much less powerful and more closely resemble humans as a species. Their powers really only consist of being able to summon a scythe (which is less powerful than that of Grim Reaper's) and faster healing- however, they do have the option of becoming Grim Reapers. Reapers are created one of two ways- they are either the offspring of a Grim Reaper/Reaper, or they were born human and turned into a Reaper by a Grim Reaper. They don't particularly have a special position in Purgatory, but most people tend to hold them in higher regard because they are usually related somehow to the Grim Reaper. Reapers can be killed like any human could be- however, they can usually withstand a bit more.