As almost everyone started to mention the most memoryable players from their own countries, I'll start from russian players. Note: I'll be egoistic and mention people by what they've done for me, not only for the whole community
1) Speedmeister. For sure, this is the guy who has done really much for russian community back then. He was a creator of one of first russian clans who still was active as hell in early 2014, he has made the "promappack" in 2006 and then asked playground.ru to create an own server with those maps special for "pro players" and we were spending our sam days there in 2007 - 2011 (and the server is still online). In 2007, he came up with idea of russian sam league which turned to the new forum "rusleague.net", which was reborned in 2008 as "leagueofstars.net" and was a home of most russian players for years .. Years later, in 2013, FoXtRoT reanimated it as a new "serioussam.su" site, but Speedy still helped with writing some awesome news on the main page.
He also organized few the real lan Sam tourneys in his city (yeah it's true, demos still exist, from 2006), and demos from this tourney were the first real pro demos which I've (as totally noob) watched in 2006 and they've changed my imagination of how SS DM gameplay should look like, I couldn't even imagine everyone plays with 3rd person, this fact shocked me so much .. And Speedy really was the best russian player in 2005 - 2007 I believe, I remember my real life friend (who always was a total noob in FPS) called me in 2008 and said "hey I was able to kill Speedmeister -)Campers(- on TLT"
Also, Speedy made his own "Serious Proffesional Modification" for SS SE 1.05 (this mod has been used for playing last season of their lan tourney) and was the main tester (and helped with much of ideas) of TeamDeathMatch Mod by Dr. Zlo. Even if those mods never were famous and totally forgotten now, this is worth to be mentioned.
2) Falcaster (aka you-know-who). This guy was probably the funniest person from GZ (and all the russian) community, an awesome example how a total trasher (Mr. Kartels) can turn up into an awesome guy. Before wearing Falcater nickname he also was "Hollow", "Liquidator", and he also was a coord there, and was doing the same things which I do now - moved russian posts to the special threads Remember it was 2008 and GZ was much more active, so this was much more hard to do Also, he recorded dat "not a big deal" parody video which is still being mentioned nowadays. xD But the main help what he did to me was fixing my shitty english (and his advices still could be useful now) posts.
3) Troy. This guy has realized my main dream when I was a child and pure nerd of Sam - creating bots for this awesome game, and more than that - due to his advices I've learned how to add bots on each map I want xD He bringed me back to Serious Editor and I even was able to create one map and started to create the second. : D Unfortunately, I'm not that young anymore and can't play 4-5 hours in a row (even when I have a time), but I was able to spend much time and improve my aim by playing with them, especially before GZ CT 2014. I was almost the only who was able to do it because STM wasn't released on public back then. So while Capri & Lexa had good tactics but pretty rusty aim (especially Lexa), I was able to do awesome shots xD And Troy is also a reason that Immortals were able to win the tourney without Destroyer for the first time. Back in the years, I've been dreaming of having bots in Sam, I was so dissapointed that games like UT (even Unreal 1) had this but Sam hadn't. I was blaming Croteam so hard for this when I was 15-16 xD When Dr. Zlo announced TDM mod in 2007, he also said he could create bots, I've kept spamming him for months but he didn't make it, unfortunately. And in six years, when Sam is close to death, this finally came - for me it was like endless waiting for Half Life 3, S.T.A.L.K.E.R., DNF etc. xD Troy is an awesome coder and also a good mapper.
4) Capricornus. This guy saved a huge amount of hours which I've been spending for counting teamkills of tournaments and teamgames by creating his awesome SS TSE Game Analyzer tool. Seriously, I never could imagine a tool like that will come. Unfortunately (same like above) this happened pretty late but anyway. And the second tool he created was Server Monitor which I still use for finding active players without running Sam (& Steam). He is another good programmer which I know
5) FoXtRoT. Yeah ! In the late 2013 he created serioussam.su and it became the new home for all the russian players, thereby a lot of russian players came back on forums and to the game, 2013-2014 winter was the most awesome, and it felt like I'm 16 again xD This guy is also a really funny person, he visited all Moscow Sam events so I'm totally sure of it The funniest thing is that we were "enemies" in 2007, because Immortals / USSR and NapaLm clans trashed each others for 24/24, and now we've friends, that's awesome and fun to remember the past together xD He is also a programmer, for Sam he created a small tool called "Name Converter" which allows convert Sam tags to bb code to have a cute signature
I also respect much other russian guys - N-Guy for being my main Sam teacher in early 2007 and organizing much of teamgames in 2013 when SeriousSam.Su created (he also wanted to create a tournament with real money prizes, but it didn't happen, seriousnikita aka Mango for invitation me to the first DM clan called "Russian Guys" (he also was a cretor of this clan, so for a while he combined a lot of newbies in the one clan), Bullet for organizing a lot of teamgames and making awesome movies, he inspired me pretty much (though I was dreaming of making a fragmovie even before this guy appeared in the community), Mitrofka for being the best leagueofstars.net moderator and the best serioussam.ru server admin, and he was one of the best persons ever, always fair, positive and never trashed, Xaeron for being the most addicted to 1v1 guy, I never liked 1v1 but he almost always made me play with him and this always was a huge fun, and for sure Destroyer, we've been playing so much together, passed through some trash wars but still friends, and even nowadays we talk and discuss everything. Much people from GZ thinks he is just a trasher but this is not true, he is a good guy. Nobody from here knows that he even organized 1v1 LT Tourney in 2011 where I was able to play my best 1v1 game ever (unfortunately this tourney wasn't finnished). And yeah, he also has mapping skills, remember his awesome (and big !) Night Town map. High Voltage is also a very cool guy and still organizing 2v2 for this old game, but the main thing for what I respect him is that he was the main guy who kept asking me about organizing a moscow events. Without him these events probably wouldn't happen.
This is not the full list for sure, I forgot about a few people I'm pretty sure, but I can't continue writing or it will never end