Although they mostly look like human beings with wings, angels have no fixed identity. They can be male or female, and are of no particular age. They are God’s messengers and attendants. They guard his throne in Heaven, act as his representatives in the human world and carry out his judgements.

Their styles of dress vary from one artist to another. And, depending what business they are on, they can look kind and gentle, or consumed with anger.

While the Angel of the North has an impressive wingspan, in the very earliest Christian art, angels tend to be wingless. It was probably felt that if they were depicted with them, they might resemble too closely certain pagan winged deities, such as Hermes (messenger of the Greek gods) or Cupid (son of the Roman love goddess Venus).

Once they acquire their wings in art, there is no stopping them, as these various examples from classical art indicate.

In The Expulsion Of Adam And Eve From The Garden Of Eden (1424-8) by Masaccio, a furious angel in red brandishes a sword and expels the wailing couple from Paradise:

In total contrast, the two bored little cherubs leaning on the bottom edge of the picture frame in The Sistine Madonna (1513-4) by Raphael look much more human. Decidedly unimpressed with the celebrity posing going on above them, they seem to be in dire need of entertainment.

Angels can also be reassuring and supportive presences, like the sturdily built adult male angel into whose arms a blithely unaware St Francis has swooned in Caravaggio’s picture, St Francis In Ecstasy.

Representations of angels can differ sharply between works by the same artist. Caravaggio paints a quite different type of creature in The Martyrdom Of St Matthew (1599-1600). Here, an angelic infant leans precariously off his cloud to offer the gospel-writer a palm branch – the traditional symbol of martyrdom

The Sacrifice Of Isaac, in which the Old Testament patriarch Abraham is commanded by God to kill his only son, was always a popular subject for Biblical art. A favoured treatment is to show the moment when God’s messenger intervenes, just in time, to prevent the killing. Of these, the Rembrandt version of 1635 is one of the most powerful.

As in other portrayals of the scene, the angel grips Abraham by the wrist at the last moment. In this image, Abraham has covered his son’s face with one hand to make the job less difficult. The angel’s intervention is decisive, and the knife has already fallen from the old man’s grasp.

Perhaps surprisingly, 20th-century art is full of angels too. Despite modern scepticism, the idea of symbolic messengers and heavenly guardians is still a fascinating one to many artists. Paul Klee’s Angelus Novus (1920) is a classic modern depiction.

Cultural critic Walter Benjamin, who bought the picture the year after it was painted, believes that Klee’s figure is the angel of history. He stands transfixed in horror at the carnage that human history is piling up before him, while his back is turned to the future.