The Emperor is the plainest card in the deck and the site of one of the strangest disputes in modern tarot. Nothing about the image is contentious: a crowned man enthroned, in profile in the older patterns, holding an orb or a sceptre. He is temporal power, and in the fifteenth-century game he sits near the bottom of the trump order with the other estates.
The dispute is about his attribution. The Golden Dawn gave him the letter Heh, the sign Aries, and the fifteenth path from Chokmah to Tiphareth. In 1904 Aleister Crowley received the text he called Liber AL vel Legis, which contains the line "Tzaddi is not the Star". Tzaddi was the Golden Dawn's letter for the Star, the seventeenth trump, and Crowley took the sentence as an instruction. His solution, worked out over decades and set out in The Book of Thoth, was to swap the attributions of the Emperor and the Star: the Star takes Heh, the Emperor takes Tzaddi, and the zodiacal signs move with them.
This is not a small adjustment, because the letters carry the Tree of Life paths with them and the whole map shifts. Thelemic readers and Thoth users generally accept the swap. Golden Dawn traditionalists and most Waite-derived readers do not, and continue to use the older assignment. There is no way to settle it from outside: the swap rests on the authority of a revealed text, and the original rests on the authority of an order that dissolved in acrimony. Anyone consulting a correspondence table for this card should check which system it belongs to before trusting it, because the two disagree and both are in print.