Sorry if this has been asked before, but I am avid watcher of the History Channel series on the Templar Knights. In one episode, the character playing the Pope announces that stories like the Holy Grail were really mysticism invented by the Catholic Church to attract Pagans to Christianity. Is there any evidence of this or was this simply poetic license?
While I know nothing about how the Church perceived the stories concerning the Holy Grail (this answer claims that the Catholic Church has no official opinion), the answer is a solid no, simply because the Holy Grail was not invented by the Church in the first place.
The first appearance of such thing as the Grail was in the romance Perceval, by Chretien de Troyes (c. 1190). This poem mentions a grail and implies that it is some sort of dish or bowl. It is not called "holy" anywhere in the poem, and is not associated to any Christian relic.
This story was left unfinished by Chretien, and four continuations were developed by different writers and, as far as I can tell, the grail is never associated to the Holy Chalice.
Wolfram von Eschenbach adapted Chretien's work into his own romance Parzival (c. 1210), which has a very similar plot to the original story, but now the Grail is a precious stone that is the sanctuary of the angels that remained neutral in Lucifer's rebellion. The backstory of the Grail in Parzival draws heavily from Christian motifs, but, again, the Grail is never associated with the Holy Chalice.
The first time the Grail is associated to the Holy Chalice is in the romance Joseph d'Arimathe by Robert de Boron (c. 1200?), which is supposed to be a prequel to Chretien's Perceval (Boron also allegedly wrote his own version of Perceval's story, that survived in its prose adaptation Didot Perceval). In Boron's story, Joseph of Arimathea receives the Holy Chalice after Jesus was arrested, and his brother-in-law took it to Britain.
Boron's version of the Grail was incorporated into the Arthurian romances in which is called the Vulgate Cycle, with some modifications (for instance, Joseph himself took the Grail to Britain, and the knight associated with the Grail is Galahad instead of Percival), and was later re-adapted into the Post-Vulgate Cycle, whose most relevant and famous version is Thomas Malory's Le Morte d'Arthur, from which most modern depictions of the Arthurian cycle and the Holy Grail derive from.
In conclusion, the association of the Holy Grail to the Holy Chalice did not originate in the Church, but in medieval romances. Whether the story of the Grail originated from the Chretien's imagination, by an unknown source or by elements of pagan mythology is still debated by scholars. Furthermore, it is worth noticing that the connection between the Holy Grail and to the hypothesized descendants of Jesus is quite recent and has no parallel in medieval literature (in which the Grail was originated).