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A shoulder angel is a plot device used for either dramatic or humorous effect in animation and comic strips (and occasionally in live-action television). The angel represents conscience and is often accompanied by a shoulder devil representing temptation. They are a useful convention for depicting the inner conflict of a character. Usually, the angel is depicted on (or hovering near) the right shoulder and the devil or demon on the left, as the left side traditionally represents dishonesty or impurity.
The shoulder angel often uses the iconography of a traditional angel, with wings, a robe, a halo, and sometimes a harp. The shoulder devil likewise usually looks like a traditional devil with reddish skin, horns, barbed tail, a pitchfork (or actually a trident) and (sometimes) cloven hooves. Often, both resemble their host, though sometimes they will resemble other characters in the story who are responsible or mischievous. In Western culture the idea develops the Christian concept of a personal guardian angel, who was sometimes considered to be matched by a personal devil who countered the angel's efforts. Especially in popular medieval dramas, like the 15th century The Castle of Perseverance. In both this and Christopher Marlowe's play The Tragical History of Doctor Faustus, of about 1592, the "Good Angel" and "Bad Angel" offer competing advice (Act 2, scene 1, etc.) to the hero.
The non-canonical Early Christian book, The Shepherd of Hermas, of around A.D. 140-150, has a reference to the idea of two Angels, There are two angels with a man--one of righteousness, and the other of iniquity. (Sixth Commandment, Chapter 2). These angels in turn descend into a persons heart, and attempt to guide a person's emotions. Hermas is told to understand both Angels, but to only trust the Angel of Righteousness. The concept is similar to ideas of personal tutelary spirits that are very common in many ancient and traditional cultures.
In traditional Christian belief, each person has a dedicated guardian angel whose task is to follow the person and try to prevent them from coming to harm, both physical and moral. At the same time each person is assailed by devils, not usually considered as single and dedicated to a single person in the same way as the guardian angel, who try to tempt the person into sin. Both angels and devils are often regarded as having the ability to access the persons thoughts, and introduce ideas.
Similar beliefs 
There is a similar Islamic belief of Kiraman Katibin, two angels residing on either shoulder of humans which record their good and bad deeds. However, these angels do not have influence over the choices one makes, and only record one's deeds. However, there is a concept much similar to the shoulder angel and devil which is of the Qareen. The Qareen, according to Islamic literature, is a personal companion and there are two with each individual, one from the angels and another from the Jinn. The word qarīn literally means 'constant companion'. The angel pushes the individual to do good and obey God while that from the Jinn does the opposite.
Modern representations 
In several modern fictional stories, a character can be marked as especially evil or mischievous by receiving similarly bad advice from both shoulder figures, having a second shoulder devil instead of the angel, or being persuaded by the devil to kick the angel out.
One may view this image in Freudian terms, with the Angel representing the super-ego (the source of self-censorship), counterbalanced by the Devil representing the id (the primal, instinctive desires of the individual).
Benjamin Lawsky, the New York superintendent of financial services, compared the plight of regulators to having shoulder angels, that "regulators operating in the specific context of the aftermath of the 2008 financial crisis had to listen to two compelling inner voices." "I think of it as really two either angels or devils sitting on each shoulder of the regulator — you can decide whether you want to call them angels or devils," he said.
In Fiction 
In the Discworld novel Nightwatch by Terry Pratchett the killer Carcer was considered by the hero Samuel Vimes to have a demon on each shoulder, but not opposing each other, just in competition to urge Carcer on to worse deeds. It was said that if Vimes looked deep into Carcer's eyes, he could see the demons looking back.
See also 
- Seiler, Casey (October 10, 2012). "Of angels, devils and regulating: Financial services chief speaks at Saint Rose on financial crisis, regulation". Albany Times Union. Retrieved October 11, 2012.