Who is Stuart Rene (Stu) LaJoie from The Moon Is a Harsh Mistress and what is their importance?

A self-styled "Poet, Traveler, Soldier of Fortune," the aristocratic French royalist LaJoie needs protagonist and narrator, Manuel ("Mannie") Garcia O'Kelly-Davis' help when he visits the moon as a tourist and commits a mortal faux pas. The situation is typical: a freely-wandering tourist reacts in "earthworm" fashion by trying to kiss a woman who flirts with him; she screams in typical Luna fashion and the stilyagi come to her rescue. Davis sees no offense but fines LaJoie $50 for ignorance of Lunar ways. LaJoie, who reminds Davis of Prof, asks about "tanstaafl." Davis responds it is an acronym for "There ain't no such thing as a free lunch"; LaJoie feels he has wandered into "Looking Glass Land." Davis invites LaJoie home for dinner and phones Mike for his dossier. He could well be the "pigeon" the Revolution needs Earthside. LaJoie leaves Luna to speculate on stocks to raise funds for bribes, dummy organizations, infiltration, propagandizing, winning over at least one major nation, and selling Lunar travel to a major cartel.