Who is the best person to beat Magnus Carlsen?

cornbread, just saw how he crushed nakamura in washington chess park

Wei Yi, ina few years time

I think Giri could challenge Magnus in a match right now, but I don't think Giri could ever win a candidates. 

Levon Aronian seems to be his toughest opponent these days.

Kramnik, if he can qualify; because he can match Magnus in the endgame and he also has better opening prep.

Caruana next and Nakamura is hopeless against Magnus Carlsen.

Let's not write off Car-Jacker.

Kramnik will be too old by the next cycle.

Karjakin is Carlsen's next big test. Carlsen doesn't have a stellar record against him, but I think Carlsen is still likely to win the match fairly comfortably. The one caveat is that in short matches such as the current World Championship accidents can happen. 

Caruana on a good day could give Carlsen a game, but I think Giri's the one who is most likely to beat him in a match of all the players currently in the top 40. Wei Yi is still many years away from proving whether he's just another prodigy who doesn't quite make it or the real thing. 

On a good day?! What is Caruana's record against Carlsen? I don't think it's that bad and let's all consider this. Fischer had never beaten Spassky prior to the 1972 world chess championship match. Alekhine had a losing record against Capablanca.

Any of these guys could beat Carlsen. The big question is will they?

Bigger upsets have happened.

Anyway, the best person to beat Carlsen would first have to qualify.

I don't think Giri will qualify next time or ever. He is still young, though, so we could see him make a drastic change.

Levon Aronian

Agreed!

Carlsen: "There are several players who I find it difficult to play against. Probably the most difficult is Levon Aronian." — CNN Interview, December 2015

Ofcouse its Hikaru.

Yes, 1-12-18 is such a high recommendation for Naka. 

Today was a great result for Naka, but it had to happen some time. I just wish it hadn't been in a Dragondorf variation. Now all sorts of kiddos will think it's actually good.

Carlsen completely misplayed it. No idea why he played f3.

Completely misplayed all the critical moments in the game. Modified the pawn structure terribly...

Amazing!! Great news!! Naka finally won!!

Alekhine never beat Capablanca before their match, and Fischer never beat Spassky... 

So now Nakamura can no longer benefit from these comparisons, unfortunately...

Komodo or maybe stockfish

His Father Henrik Carlsen:

I have a theory it will not be Nakamura because his record against Carlsen in full length games is very bad, even with a recent win.

I think the post that says the person to dethrone Carlsen is going to be 5 years younger at least.  It will certainly be someone younger imho.

In fact it may be that a lack of dangerous rivals may prevent Carlsen reaching his full potential !  No I mean it.  It may have been "better" for him if he had been 10 years older, when he was looking at trying to become world champ he would have been confronted by younger and more dangerous versions of Anand, Kramnik and Topalov, not to mention Kasparov.

I believe Anand still has a last chance. Aronion is a solid competitor. If you are asking who is most likely to draw with Carlsen that would be Giri. Wei Yi and Wesley So have some time to beat him. Nakamura just beat him recently. Topolav has no chance and we will see if Alexander G. can beat him in the Grandmaster Blitz Battle Championship!