The Tregetour does not appear in Paris, but was added by John Lydgate. Jon Rikelle might have been a historical person related to the Rikhill's that lived in London at that time.
A "Tregetour" is what we today would call a conjuror. Strutt, in the book "Sports and Pastimes", 1801, writes: »The name of tregetours was chiefly, if not entirely, appropriated to those artists who, by sleight of hand, with the assistance of machinery of various kinds, deceived the eyes of the spectators, and produced such illusions as were usually supposed to be the effect of enchantment; for which reason they were frequently ranked with magicians, sorcerers and witches; and, indeed, the feats they performed, according to the descriptions given of them, abundantly prove that they were no contemptible practitioners in the arts of deception«.
Lydgate's contemporary, Chaucer, wrote about the legendary magician, Coll:
Ther saugh I Colle tregetour
There I saw Coll, the conjuror
As Strutt writes in the above quote, the line between a conjuror and a "real" magician was blurred in those days. On one hand the text refers to legerdemain: »sleightes and turnyng of thyn honde«, »illusiouns« and »Legerdemeyn«. On the other hand, you feel the power of the sorcerer who knows about the course of stars: »cours of sterres « and the influence of the (starry) sky: »of the heuene al the Influence«.
And just for the record: It's King Henry, who's the conqueror - not Jon Rikelle.