The Devil is a character which shows up in multiple mythologies. Though Loki is frequently compared to The Devil, that isn’t a great comparison. Loki isn’t a god of temptation, he is an amoral god who just does stuff until people get mad at him and he has to fix it.
You will recognize the man and the woman from The Lovers in the Waite-Smith version of this card. They are trapped at The Devil’s feet. They have horns and a tail now, because they have been trapped by their lust. The top of the woman’s tail is a thistle or a raspberry, and the man’s tail has a flaming tip.
The Devil has his hands in the same position as The Magician, but his arm is bent: he is not reaching as high. Also, he holds a torch in his left hand, which he lights off the burning tail of the man.
The Northern Germanic mythos just doesn’t have the same concept of “sin” that the Christians do. The Devil is a card of ᛜ and ᚦ (Inguz and Thurisaz): the conflict surrounding masculine sexuality. Like Thurisaz, The Devil is often “A pain to women” in the sense that lustful acts can lead to unwanted pregnancies.
The Fool’s Journey
The closest to The Devil in Norse Mythology is the story of Gullveig, whose name literally means Gold Greed. The Vanir goddess Gullveig was burned at the stake for teaching men to love gold, but then she came back from the dead and continued telling men to love gold. This temptation could not be killed by fire, so the Aesir went to war with the Vanir.
The most important symbol on The Devil is the symbol of The Horned God. The Aesir do not have a horned god, per se, but Frey comes close to most depictions. The Horned God (Pan, Herne, etc.) is frequently associated with sexuality and lust, traits also strongly ascribed to the Vanir god Ingvi Frey and the rune ᛜ (Inguz). Though I haven’t seen it in a Tarot deck, many images of The Horned God show him with a large, erect phallus, similar to the famous statue of Frey shown below.
Another important symbol of The Devil is the chains he uses to bind you. These chains don’t tend to be tight; they are chains you choose to wear in order to sate your lust, pride, or other “sin.” In The Giants Tarot (right), you might say that the chain, Gleipnir, looks tight on Fenris, but Gleipnir doesn’t bind Fenris: it binds Odin to his fate. The chain is loose around Odin because it is so tight around Fenris.