The term angel of death is pretty broad, and may refer to numerous different beings or entities. With Christianity, the archangel Michael is often referred to as the angel of death. Within the Roman Catholic Church, the archangel Michael, or Saint Michael as he is often referred to, has four primary duties or tasks that he is responsible for. One of those duties is that he acts as the angel of death, carrying the departed souls of the dead or deceased into heaven. Once Michael and the departed soul reach the heavenly gates, the soul is then judged by Michael, which is the reason in art he is often depicted holding scales. As the legend goes, Michael arrives upon the hour of death, and then gives the soul the chance to redeem itself. While Michael escorts the soul, Lucifer and his demons usually try to intervene, so that they can persuade the soul to follow the Prince of Darkness into hell. There are many Renaissance paintings that show this set of events.
With regard to Islam, the angel of death usually refers to Azrael, who is also called the Archangel of Death. Outside of traditional Islamic beliefs, Azrael is also regarded as the angel of death in Islamic extrabiblical tradition, as well as in secular Islamic folklore. If you come across the name of Azrael within English Islamic text or scripture, you will sometimes see his name spelt Azra'il, Azra'eil, Izrail, Azrail, Ezraeil, Ozryel, Izrael, Azrin, Azriel, Azryel, or Azraille. Despite the numerous spelling variations, they all refer to the same angelic entity. With regard to this celestial being's function, he is usually depicted as the personification of death itself in the broadest of terms. Azrael is also believed to be under the direct command of the will of God himself. It is also said that he will be the last to die, so that he can carry on the work of meticulously cataloguing every single life and death that has ever taken place throughout all of time.
In Judaism the term angel of death mostly refers to Gabriel, however it can also refer to Samael and Sariel. In ancient Hebrew scripture, as well as noncanonical Jewish literary works, Gabriel often fills the same role that Michael does in Christianity. When a person dies, Gabriel descends from the clouds to guide the departed soul to heaven. Upon reaching the gates of heaven, Gabriel will judge the soul's worthiness, and either walk them into heaven, or cast them down into hell. As far as Samael is concerned, he is a high ranking angel who acts as a seducer, destroyed, and accuser, a figure that is often affiliated with both good and evil. It is also believed that Samael was the personal guardian of Esau, the patron saint to the mighty Roman Empire. The archangel Suriel is another renown Judaic character that is also known as the benevolent angel of death, and it is said that he personally guided the departed soul of Moses himself into the afterlife.
Outside of the three Abrahamic religions, the angel of death is quite a common figure in myth, folklore, and pop culture. In fictional literary works there are almost an unlimited number of reference to this figure, such works include the Angel of Death novel by Jack Higgins, and another of the same name by Alane Ferguson. In film and digital media there have been tons of works entitled the Angel of Death, spanning across many decades. Strangely, real people themselves have often been labeled the angel of death by society, after they have committed evil deeds. It is not known exactly when this gloomy figure first came to use, but archaeological evidence suggests that similar characters are traceable all the way back to the dawn of civilization. The ancient Egyptians have several different figures responsible for guiding departed or lost souls through the underworld, as did the Romans, Greeks, Babylonians, and the Persians.