Alex "Neeb" Sunderhaft -- Neeb is one of the youngest players in the World Championship Series and has been playing competitively since the beginning of Heart of the Swarm. He started off as a Terran player and despite his youth and inexperience has generally had good results in WCS North America. After some time, though, he eventually reached the point all players come to when they get tired of playing the same race. He then looked up into the sky and remembered when Kim "Classic" Doh Woo used to play Terran, lost to Marcus "Thorzain" Sebastian Eklöf in Proleague, switched to Protoss and eventually became a GSL and StarCraft II StarLeague Champion.
Or maybe he just really liked DTs. Whatever the case, Neeb switched races once Legacy of the Void came in and has become a much better player for it. While most of his results are online, he has shown enough skill that he is a player to watch out for to see how he does on a big stage when he as a real chance of going deep.
Choi "Polt" Seong Hun -- There are a lot of things you can say about Polt. He has had incredible longevity and has been playing StarCraft II since the Global StarCraft II League Open Season 1. He is one of the best players all time. The number of players that approach the game the same way he does can be counted on one hand. He has survived every patch and expansion thrown his way and has shown that even in the most imbalanced eras (BL/infestor and the Blink era), he is one of the few you can count on to find a way to win.
On the other hand, his prime passed him nearly a year ago. Ever since his victory in WCS Season 1, he has been on a steady decline in both results and skill. However, what makes Polt remarkable and so interesting to watch is that he thinks about and tries to solve the game. His entire history has him losing to a player multiple times (Stephano, Scarlett, Hydra) before figuring out how they play and beat them. It is the exact same when it comes to his bad matchups. While he isn't nearly the beast he was back in 2014 and in early 2015, he is still dangerous. He is still one of the great champions.
Théo "PtitDrogo" Freydière -- After winning DreamHack Leipzig, PtitDrogo became the new French hope as he overshadowed David "Lilbow" Moschetto WCS run in 2015 and Alexis "MarineLord " Eusebio's victories over Korea in Nation Wars. PtitDrogo's notable victories at DH Leipzig were over Neeb, Dario "TLO" Wünsch and Aleksandr "Bly" Svusuyk. And while the victory there was good, the problem was that not everyone was in attendance so it was impossible to make a judgement call as to whether he was really the best player in WCS or just the best player who was there on that day.
To complicate matters, the patch hit post-DH nerfing Protoss, and this has given PtitDrogo trouble adjusting as he started dropping online series to multiple Zergs. Despite that, just in terms of pure gameplay, PtitDrogo has one of the cleanest Protoss play styles in WCS, he approaches the game in a unique way and he is still one of the favorites to contend for a championship.
Zhou "iAsonu" Hang -- Among the various national scenes in SCII, China has always been the most isolated. Even far off places like Australia or Taiwan have usually had at least one player represent them in international events like Moonglade or Sen. In China's case they were landlocked to China barring a few WCG's until the implementation of the WCS system in 2013. Since then they've been released unto the world leaving players and spectators shocked at how strange the metagame evolved within China. Their metagame was akin to an insane asylum and the Chinese region as a whole produced some of the strangest, funniest and most captivating games anywhere.
And in that chaos, Jim and MacSed were the favorites to come out of China until 2015. In 2015, iAsonu usurped their position as the best player from China and has held that spot ever since. Though we haven't seen much of him since WCS 2015, there is one interesting point to make. Lilbow eliminated him in season 3 and eventually went on to become champion. Lilbow decided to not practice HotS and instead practice LotV to win Golden Professional League 2015. Coincidentally, iAsonu decided the best way to get his revenge on Lilbow was to only practice LotV and eliminate Lilbow from that tournament, which he eventually did. While the brackets line up in such a way that they can only meet up in the finals, it would certainly be a rematch with just that extra bit of spice to it.
Ke "Has" Yu Feng -- There are certain players out there in every scene, in every game. Anyone who has ever played something competitively online for a meaningful amount of time has met them. There are players whose sole existence seems to be to annoy you, rile you up and troll you. There are those types of players and then there is Has, who is unlike those other plebians. You see the others are forced to use words, messages and out-of-game actions to annoy you. Has merely has to play the game. When other players cheese you, there is an implicit understanding between both players as to what is going on. When Has cheeses you the only thing you understand is that it is coming. You do not know how and you do not know why. Has doesn't just cheese the player he's playing against, he's cheesing the caster, the analyst, the observer and the audience all at the same time.
There is almost something artistic in the way he does it. You think to yourself, surely he can't one-up his triple cannon rush or his hail mary 4 DT rush can he? And then he 7 pylon rushes Lee "Jaedong" Jae Dong out of WCS. There is no one more dangerous than Has in this tournament. Not because of his skill, but because he is the best at stealing wins from anyone who is better than him in surprising and perplexing ways. It is no surprise that the Taiwanese have given him the nickname the King of Cheese. An incredible player to watch for anyone (so long as you aren't the one playing him) and living proof that evil can succeed even when good men do something.