I'd like to say Giri, but I am starting to doubt that anyone will beat him.
Who is the best person to beat Magnus Carlsen?

N59690-"Donald Trump can, His IQ is one of the highest, and you know it, plus he undestands the chinese mind, he's made a ton of money with the chinese mind"
I hope you were being sarcastic with this ignorant comment... lol
He's just trying to increase the views on this thread because he wants to invite a good portion of people who were looking at the forums waiting for a moment to say that Donald Trump is racist and should be killed.
Richard Rapport is another youngster with an unusual style. So he may be able to beat Magnus.

Richard Rapport of Hungary is six years younger than Carlsen and already rated over 2750 and in the World's top 20.
However, the best way to judge a player's potential is to look at their games. To do that with super-GMs you need to be a strong GM yourself. Unfortunately I am not and almost certainly never will be.

Anish Giri has been sharpening up his game lately. He's been winning and losing more games this year than last. He, Naka and Caruana are probably the three most likely to challenge in the next cycle, though I'm also rooting for Kramnik to continue his fine form.
I don't expect much from Karjakin next month. And, I'm rooting for Carlsen to beat him decisively. One of the hallmarks of a great world champion is the ability to win or hold the match-play title against different opponents. The World Champions who have done that include Steinitz, Lasker, Alekhin, Botvinnik, Petrosian, Karpov, Kasparov, Kramnik, and Anand. Carlsen has a chance to join that elite group by beating Karjakin.
In terms, of engaging in a 'marathon' chess match.. Where 'ability' is the Only pre-eminent 'factor'?! .. Then, you're looking at 'komodo's, last, or latest, {software}, 'upgrade'! o:

In terms, of engaging in a 'marathon' chess match.. Where 'ability' is the Only pre-eminent 'factor'?! .. Then, you're looking at 'komodo's, last, or latest, {software}, 'upgrade'! o:
A chess match should be at least 16, but anything over 20 is probably too much.

Anyone can beat Magnus. Anyone can beat anyone, that is one the joys of Chess. He is actually looking a little more vulnerable these days in his play. That being said, I do not think Car-Jacker will be the one to dethrone him. Perhaps, by the next cycle a real challenger will emerge.
I am hopeful by then that Chess will be have moved to Chess960 model. I want to see the person with the greatest ability, not memory, be the World Champion. Magnus, as a gifted natural player, would still likely be on top, with Docamura a close second.

He's going to retire unbeaten like Floyd Mayweather forget about it.
Sorry but Magnus won't get to duck and cherry pick like Floyd, or Lasker.
It perfectly fits the 10000 hours rule. Learned chess at 15 and GM around 25.
It's even more amazing that he managed to win the world youth U12 before learning how to play chess.