I grew up in Brazil and I used to visit and marvel at the beautiful coast where the movie was filmed. The area is called "Parati" and is part of the "Green Coast" of the Rio de Janeiro state. It is some 150 miles from the Rio de Janeiro city.
This movie brings back to life the world of 16th century Brazil, where Europeans were barely starting to explore the coastline, which was still in pristine state and sparsely populated by various native tribes. French and Portuguese fought each other for territory and for the upper hand on the Brazil wood trade, all the while negotiating with the natives, who also fought each other for whatever reasons.
One French misfit ("a mercenary") is left to die by his own compatriots but manages to escape and is kept prisoner by an all-naked native tribe. While he is a "slave" of the chief, according to the customs of the tribe, he is allowed to live in relative comfort for months until the time is right for him to be killed and eaten in a ritual of revenge.
What I love about this film is that it recreates in loving detail the natives' villages and their way-of-life (they walked naked and were cannibals) and asks us to recognize and accept the life in those times as it was: in a gorgeous garden-of-eden, life was messy, violent, full of pathetic superstition and bizarre customs. The Europeans arrive and bring their own problems, including more violence with better weapons and greed. There is no romanticized "noble savages" or "heroic explorers" here, it is just people trying to survive in a tough world.
The movie is neither unduly sympathetic nor dismissive of the natives. From what I know of the subject, the depiction is fairly accurate which adds an air of uniqueness to the project: how many movies have you seen regarding the lives of Brazilian natives and their early affairs with Europeans?

Another turgid action/adventure flick from the Quinn Martin Productions factory. Roy Thinnes plays undercover agent Diamond Head (Mr. Head, to you), working for his G-Man handler "Aunt Mary", looking for "Tree", who's on a mission to...well, just watch the movie.
This one deserved and got the full MST3K sendup. As the boys and various reviewers have pointed out, the movie "Fargo" had more Hawaiian locations than this film. Apparently shot on a puny budget, this movie highlights Hawaii's broken-down dive shops, gas stations, and cheapo hotels. Zulu -- later to star as Kono in Hawaii-Five-O -- appears as Thinnes' lumpy, inept sidekick, while France Nguyen models the Jenny Craig diet gone horribly wrong. Others sharing the flickering screen include a drunken Richard Harris knockoff, a George Takai imitator, a not-so-smart hit-man with sprayed-on Sansabelt slacks, and the villain "Tree", sporting a veddy British accent. You can pretty much figure out the plot halfway through the opening credits, but relax--just enjoy the giddy mediocrity of this 70's movie-of-the-week.
Whenever I think of this movie (and I think of this movie often), I catch myself humming the theme, written for flute and tuba...no one knows why.
Trivia note--Diamond Head was directed by Jeannot Szwarc, one of three contract directors at Universal who would go on to make much bigger films, in his case Jaws 2. The others were John Badham (War Games), and a young fellow named Steven Spielberg...