An episode of Kolchak: The Nigh Stalker featured a swamp creature known as ‘Père Malfait’. (‘Father Evil Fact’? ‘Father Poorly Done’?) Does Père Malfait exist as a bogeyman legend, in the way that there are legends about Bigfoot, the Bunyip, and the chupacabra, for example? Or was Père Malfait something invented for an episode of a TV show?
“Père Malfait” = “Father Does-Evil”. Malfait appears to be a not-uncommon surname, and the most common word for boogeyman I know is croquemitaine, but you find things like “Maufait : ou MAUFÉ (mô-fé), n. m. Nom du diable dans tout le cours du moyen âge.” Mau- is a reguar outcome of mal- in this environment, and the rest says roughly “A name for the devil throughout the Middle Ages.” From here
Looking it up as… contiguous… Malétroit in Google only lists the Stevenson short story, ‘The Sire de Malétroit’s Door’, which indicates that it was invented for the purpose by him despite sounding as maleficently mediaeval French as all get-out.
I love Kolchak. My mom and I used to watch it when i was little (6 or 7) back in the 1970s. I also own the series on DVD and pop it in from time to time. I also live in New Orleans and went to college in Lafayette (Cajun country) and never heard of Pere Malfait outside of the Kolchak episode. The only “boogey man” I ever remember hearing about in this area was the Loup Garou. There is even an artistic “rendering” of the Loup Garou in the Louisiana Swamp Exhibit at the Audubon Zoo here. I also remember hearing about the Honey Island Swamp monster when I was a kid, but I think that was just from a movie or something.
You might also be remembering stories about The Fouke Monster.
This was the inspiration for the movie The Legend of Boggy Creek.
Hell, when I was a kid, just the commercial for “The Legend of Boggy Creek” would scare the crap out of me. I had nightmares and never saw the actual movie.
I had the same experience as a kid. 
I saw the movie. The monster knocked over some flower pots (off camera) and that’s about it. The commercials were probably scarier.
I don’t remember where I heard of the loup garou, but it’s one of the things I like about the band Loop Guru. Not werewolfy, but I like the pun.