Since it's inevitable that I will have missed something or made a mistake in this video, this pinned comment will be updated with any new information or corrections that need to be noted, with the most important at the top:

(1) Ulrich Unhold's primary source has been confirmed! The Orient Expedition board game instructions call him "Sam Sinister" in every language except for German, which calls him "Ulrich Unhold". Thank you @user-mt2vi6dp6o for pointing this out! I can't believe it was staring me in the face for 21 years and I've never noticed it before...
(2) @catalogues4741 has uploaded a 4K version of the 1998 Danish catalog video and confirmed that the pilot is named Harry Caine, not Harry Cane. I'm very sorry for the misinformation in my video.
(3) The primary source of Alex Gluipstra, Alexis Gluipstra, and Sluwe Jacques has been confirmed! Thanks to Makreel on BrickLink, I've confirmed my hypothesis that all three names are used in the 2000 Dutch catalog.
(4) I extensively covered the Sam Sinister Switcheroo and the Harry Cane Switcheroo, but I forgot to mention that there's also a Johnny Thunder Switcheroo! On the 2001 online LEGO Shop, the product description for 5902 River Raft seemingly refers to Rudo Villano as "Johnny Thunder". This is especially odd, since the 2000 LEGO.com page had a different product description that correctly identified Rudo Villano.
(5) It's possible that "Sanister" is intended as a pun on the surname "Banister/Bannister", which makes it more clever than I give it credit for. But I still think it looks like a bad typo, so maybe the pun would've been clearer if it was spelled "Sannister".
(6) Why is Pharaoh Hotep missing from the group shot at the end of the video? Funny story about that! I've owned all the Dino Island and Orient Expedition minifigs (plus Harry Cane) firsthand since 2000-2003, and I acquired Slyboots and the Jungle minifigs secondhand more recently, but Hotep was the only named Adventurers character that I never owned. But then, just one week after finishing this video, I finally acquired a Hotep minifig and completed my collection!
(7) One article of the Summer 2015 LEGOLAND Times uses a picture of Jake Raines' minifigure to represent "World's Greatest Adventurer", further muddying the issue of whether the World's Greatest Adventurer is supposed to be Johnny Thunder, Jake Raines, or a mashup of the two characters.
(8) As verified by @simenon5929 and @JB-ey4mi, the French Dino Island commercial is definitely saying "Johnny Thunder" and not "Johnny Tonnerre".
(9) Although I showed English scans of World Club Magazine in 2000, I forgot to specify that these scans come from the Australian publication. And while it's shown in the video, I did not mention that both "Sam Sanister" and "Sam Sinister" are used in different issues from that year: Sanister in Number 2 (38:12) and Sinister in Number 3 (34:44).
(10) Bricks To Bytes has two different versions of the LEGO Chess FMV script. I showed one version in this video, but the other version appears to be an earlier draft with some minor differences, most notably the fact that Dr. Kilroy and Pippin Read are called "the Prof" and "Pippa Grant".
(11) As verified by @Reitid, "Villám Tamás" should have been translated as "Thomas Lightning" instead of "Lightning Thomas".
(12) The box flap for 5976 River Expedition has text in English, French, Spanish, and Portuguese. Curiously, only Portuguese translates Johnny's name (Johnny Trovão) like other sources, whereas French and Spanish retain the English name instead of translating it to Johnny Tonnerre and Johnny Trueno.
(13) Jungle Explorer appears in LEGO Fortnite. The bad news is that he has a new name: Sawyer. The good news is that he mentions that he also goes by Johnny Thunder, Sam Grant, and Joe Freemann.
(14) Johnny Thunder returns in the new 2024-2025 City "Explorer" subtheme! In the 2024 jungle subtheme, he is unnamed in official media, but fortunately model designer Rik Pauwels directly refers to the minifigure as Johnny Thunder on Brickset. In the 2025 arctic sets, he is finally explicitly named Johnny Thunder in the product description of set 60470.
(15) According to LEGO.com building instructions, Johnny Thunder's name in Slovenia was translated as "Janez Grom".

A separate section for anyone who was mistakenly left uncredited in the video itself:
(1) Although the YouTube channel @ireallydontcarewhatthisis was properly credited, their Internet Archive account "I can put anything in this text field oh sweet" was accidentally uncredited.
(2) Nostalgist's Archive on the Internet Archive was uncredited for their high-quality scans of Kabaya box art.
(3) It's Fun 4 Me! was uncredited for the image of the LEGOLAND Hotel Treasure Hunt.

You know we've hit Peak YouTube when a channel with less than 1,500 subs puts out a video on an obscure Lego minifig character from a long-extinct theme line that's almost as long as the first X-Men movie.

its my sleepover and i get to pick the movie

As a media preservationalist, it pains me to say that it's actually very thematic, that Adventurers has so many misconceptions, misnomers, and lost media. It really is the Lego equivalent of ancient history with pieces of information that have yet to be put together.

It's now my headcanon that Slyboots was the original Sam Sinister, and that he had a tragic Indiana Jones-esque villain death at the end of the Egypt subline, and Baron von Barron assumed his identity in order to claim Slyboots' estate and double his own wealth.

It's funny, I always knew Sam Sinister was two guys and Baron von Barron was only one. But somehow I had never heard the name Slyboots!

Ive come to the headcanon that baron bon barron and not-a-lord sam sinister used to be accomplices, but barron murdered sam and took his identity for nefarious, monetary gain.

I am horrified and incredibly disappointed to hear that such important LEGO resources as Bricklink are using incorrect information, based on a non-canon book. 😢 Can't trust anyone these days. 😡

May I have your attention please?
May I have your attention please?
Will the real Sam Sinister please stand up?
I repeat, will the real Sam Sinister please stand up?
We’re gonna have a problem here.

One thing to consider Lord Barron's switch from a pith to a tophat: Imagine instead it's a beaverskin cap or similar. Something he normally wouldn't wear, but it's the mountainous orient. The crews met a yeti. It's cold. He probably changed because he didn't want to freeze. Something Kilroy probably bemoaned in private.

As I started with Lego in 1998, to me Slyboots is Sam Sinister where as Baron von Baron is the correct name for the one with monocle and hook hand.

As a native French speaker, I can confirm you again that the French commercial does say "Johnny Thunder", just like the English version. We always knew the character as such.
Really good video, keep it up!

My theory on the name change comes from the alt build for "Oasis Ambush." Where it shows Slyboots as a skeleton. I believe that Baron went to Egypt thinking he would score big, and it would elevate his name. But by the end he was embarrassed by his losses and even lost a henchman. So with Slyboots dead, he took his legal name Sam Sinister, and continued his adventures, eventually changing his look to resemble Slyboots as to draw suspicion away from the Von Baron family. His sister is either Slyboots sister or is playing along with him

This is the Lego version of the yellow lightsaber kenner put out for Luke. Love it

I knew that Adventurers’ localization was confusing, but not THIS confusing! It seems wherever in the world you were, you had to deal with inexplicable name changes. I remember being mightily confused as to why Sam Sinister was called Mr. Hates in Lego Island 2—that was probably the only piece of media with that name that reached the United States.

The use of “Sanister” for Sam and Alexia has to be the most bizarre choice though. I truly don’t know what they were thinking there.

What is this? A 1.5 hour long video from a channel i dont know,  about a lego-series i have never heard of, about a lego-series lore question i have no idea about? at a time where i really should go to bed instead? well i will be damnded youtube, i will watch it right know!!

Mate, you include a lot of materials from around the world, to just depict a differences of few plastic figures to what is right and ''canon''... brilliant work, You have done a lot of research and made very good  video montage ❤

I always thought Pippin Reed was another pun name, just not weather related. Pippin closely resembling Piper, like a musical wind instrument. And Reed, the bit on the end of most wind instruments.

This is my absolute FAVORITE LEGO lore video on Youtube. And I've watched alloooott of videos like these.

Videos like this are what I love about Youtube. I've been around, but a lot of this information is still new to me. Excellent work compiling all this!