The Devil is missing. Neither a Devil nor a Tower survives in the Visconti-Sforza decks, the oldest substantially complete tarots we have, and there is no way to establish whether they were painted and lost or never painted at all. Given how many other cards from those decks do survive, the absence of exactly these two is at least suggestive, and it is regularly cited in arguments about how the trump sequence was assembled. It settles nothing, and anyone stating confidently that the early tarot had no Devil is going beyond the evidence.
What is certain is that the card's modern appearance is Victorian. The horned, winged, goat-headed figure with a torch, a reversed pentagram on the brow and a pair of small chained figures below descends from a drawing Eliphas Levi published in the 1850s, his Baphomet, which he composed from several sources including the accusations made against the Knights Templar. That figure was then absorbed into occult tarot and became the standard Devil. The earlier French card shows a horned figure on a pedestal with two smaller figures bound to it, which is the same structure but not the same creature.
The Golden Dawn assigned the card the letter Ayin, the sign Capricorn, and the twenty-sixth path from Tiphareth to Hod. Ayin means an eye, and the connection usually drawn is to appearances and to seeing wrongly, which suits the card better than horns do.
So a modern Devil card is a fifteenth-century composition wearing a nineteenth-century face, and the face is the part everybody recognises.