The first Tisroc (Claimed)
the Tisrocs and Tarkaans and Tarkheenas (claim descendants)
Tash is the patron god of the ruling class of Calormen. The Calormene capital is named Tashbaan, and the Tisrocs and Tarkaans and Tarkheenas all claim descent from Tash. The worship of Tash is the only formal religion depicted in the world of Narnia, except that the people of Narnia honour the memory of Aslan, a great lion who was killed and returned from the dead many generations before. There are temples to Tash, Calormenes regularly use ritual phrases such as "Tash the inexorable, the irresistible" and "Tash preserve us", and he is the only being referred to by any character in the books as a god. At the end of the series, Tash is revealed as the antithesis of Aslan (who represents Jesus), and appears as a terrible demon, with a skeletal, humanoid body, a vulture-like head, and four taloned arms.
The Horse and His Boy
In The Horse and His Boy, which explores Calormene society in some depth, the name of Tash is frequently used in oaths and exclamations. (Two other Calormene gods are mentioned, Azaroth and Zardeenah, Lady of the Night and Maidens, but only briefly.) However, Tash is not described at all, and his worship plays little part in the proceedings. Near the end, the principal antagonist Rabadash, frustrated and maddened by defeat, tries to call on Tash to inflict vengeance on the Narnians and Aslan—such as "lightning in the shape of scorpions". But this results in nothing but mockery and pity from his captors, because Aslan, after repeatedly warning Rabadash to repent of his anger, turns Rabadash into a donkey. Aslan tells Rabadash that his transformation will be lifted when he visits the temple of Tash in Tashbaan during the middle of a festival (meaning he'll be seen changing back by thousands of people), and that afterwards he must never stray more than ten miles from the temple or he will be transformed again, this time with no ability to return to his human self.
The Last Battle
The worship of Tash persists in The Last Battle, the final book of the series, in which he is depicted as a malevolent and real being who is the antithesis of Aslan. Narnians distastefully describe him as a god or a demon. Tash appears much larger than a man, with four arms and the head of a vulture; his presence brings cold and the stench of death. While the Calormenes offer human sacrifice to Tash, a majority did not actually believe in him. Illustrations by Pauline Baynes enhance his macabre appearance.
In the course of the story, the Calormene warlord Rishda schemes with Shift the manipulative ape and Ginger the duplicitous cat to concoct a story that Aslan and Tash are the same being, called Tashlan. Many Narnians see that this is ridiculous, given the antithetical nature of Aslan and Tash, but they are powerless to contradict the Calormene soldiers. The conspirators also send dissenters "to meet Tashlan" in Puzzle's stable, where they can be secretly murdered – though they are unaware that they have actually summoned Tash into Narnia. Ginger encounters Tash and barely escapes, losing the power of speech. A devout Calormene soldier named Emeth enters the stable, determined to meet his god; he kills the Calormene soldier waiting to dispatch him and vanishes into Aslan's Country, where he meets Aslan and realizes where his true devotion lies. When Shift is thrown into the stable, Tash devours him. Rishda takes fright at this, and hastily attempts to save himself by offering the remaining Narnians as sacrifices to Tash. Tash appears one final time when the Narnian king Tirian drags Rishda into the stable, and the demon seizes the warlord before High King Peter banishes him in Aslan's name back to his own realm.
When Emeth meets Aslan, Aslan tells him that "all the service thou hast done to Tash, I accept as service done to me" and further explains that "no service which is vile can be done to me, and none which is not vile can be done to him". He explains that Emeth's pious devotion, because it was rooted in a love of justice and truth, was really to Aslan rather than to Tash.