<P> In The Simpsons episode Whacking Day Homer presents the concept that everyone has a good and a bad self to Lisa, who then imagines Homer's evil version dancing on the grave of good Homer while singing' I am Evil Homer, I am Evil Homer', implying that within him the battle for good and evil has long ago been won by his bad angel . </P> <P> 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 rather than an angel and a demon, 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 . </P> <P> The Adventures of Tintin comics used this concept in at least two stories The Red Sea Sharks, where Captain Haddock's good and bad angels try to convince him to drink a bottle of whisky . The bad one is able to convince him, but the bottle smashes before he is able to drink it, leaving the good angel victorious . In Tintin in Tibet Snowy is tempted by his demon to lap up Captain Haddock's whiskey leaking from his rucksack or enjoy a huge bone rather than deliver a vital message . His good angel loses the argument leaving in tears, and he gnaws the bone while the message blows away . Realizing his mistake, Snowy makes amends by reaching a local monastery and brings the monks to help . </P> <P> In both examples, the angels resemble good or bad versions of their subject, with horns and angel wings . </P>

Where did the angel and devil on the shoulder come from