(Preface: sorry I know this thread is two months old but seems like the issue may still be open)
This post made a lot of sense to me so I'm making my comments based on agreeing with Dan's approach, particularly the idea of "special reasons". Based on that, I'd have the following nominations:
sierk - I think this is pretty self explanatory but anyone let me know if you disagree. Maybe he was initially left off as a conflict of interest? If he was, I think it shouldn't be anymore
8Freak8 - I think Lawrence was one of the most impactful GMs - he is largely responsible for the "professionalization" of Habbox's operation (which I know people may argue about whether that was a good thing) but looking at the forum today it's undeniably a lasting legacy - I think this is the differentiator for him. In a large way, ---MAD---'s tenure was a continuation of the work 8F8 began, and 8F8 left a lasting impression on many of the other managers who worked for him as well.
DJ-3000 - DJ-3000 was undeniably one of the giants of early Habbox, along with Mizki, Sierk, MissAlice, and Jrh2002. His "special reason" would be that he was the driving force for putting HxHD on the map when he took it over from Mizki in 2004. He was the first "new hire" manager for HxHD, HabboxRadio, and the Forum (all of which he ran simultaneously) after taking them over from Mizki, Mizki, and Jrh2002 respectively. He had a contentious split with Habbox in late 2005 where he took the help desk with him (rebranded and created a new forum) but Jrh2002 did the same thing - though unlike DJ, Jay later reconciled with Habbox. Regardless, DJ-3000 is a massive figure in Habbox History and should be on there.
Jin - Jin has always been someone who gets stuff working in the background but has been instrumental to Habbox in many ways, including being the backbone that kept the site up through many server issues and DDoS attacks over a several year period, and most importantly, stepping in as owner to prevent the site from going down when sierk was no longer able to do so. If that's not a significant contribution I don't know what is (as a side note, I'm somewhat biased as I'm closer to Jin than most of the other people that I listed, but I think it's a fair point.)
MattGarner - Matt actually is the longest serving GM and did a lot for Habbox in my time working with him. I'm probably less of an expert on his tenure as GM than other people who have already posted, but what I will say is that from my point of view he was handed Habbox in an especially difficult time and made a valiant effort to move things to the right track. (This too is probably biased slightly by the fact that I think Matt's awesome, but I tried to be as impartial as possible)
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doraemonkiller may be another candidate for this list. @-:Undertaker:- - I would also be very interested on your take here. Even though he doesn't have the same "fame", I seem to remember him as one of the early faces and driving forces of putting RV on the map initially, as well as being around for quite a while to drive RVs forward, but you probably have a more qualified opinion here and I'm not sure if my memory is entirely correct on this one.
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On the topic of members being in HoF, I also think it shouldn't necessarily be limited to members of staff, but I get the point that it's difficult to identify what a member who "contributed something outstanding" is. This is particularly true because the Habbox community has always had different sub-communities, and there are very few who rose above those as an "elder" respected across the community. If we were specifically looking for community members, two would come to mind.
GommeInc - Gomme I think is the exception to what I said above, which was someone who was very widely respected across all parts of the community. I would even go to say that after MissAlice, he might have been one of the most widely respected members of the community ever. He also held large sway among staff when he gave feedback because of his impeccable reasoning but also the knowledge that he was in many ways a moral center of the community. Maybe this is swayed by my perspective as being a staff member, and he wasn't viewed the same way among members, but that's definitely how many of us saw him.
FlyingJesus - I think the particular thing that distinguishes Tom is that he was actually formally recognized as a champion of the community's interests in his roles on the Habbox Council and I believe as Community Manager when we did the FM to MM / CM split. In both of these roles we sought out people who were essentially "community leaders" to elevate forum members to positions where they were given additional access to management in order to represent the community's interests.
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As a side note, if you do end up editing it, would recommend having a content designer (do those still exist?) using this thread (its in the staff forum, sorry) to do some fact checking (though even more authoritative would be searching for the actual announcements threads). For example, the comment about ---MAD--- being the longest serving GM - MattGarner is definitely the longest serving GM and even of the first four GMs (previously Site Managers) (properclone, 8F8, ---MAD--- and myself) all four of served 14-15 months according to that thread (which is actually kind of eerie).