Original: He has been ranked number one a total of 27 months in his career, fourth all-time since the inception of the FIDE ranking lists in 1971 behind only Garry Kasparov, Anatoly Karpov, and Bobby Fischer.
Simplified: He has been ranked number one a total of 27 months in his career, the fourth longest, behind only Garry Kasparov, Anatoly Karpov, and Bobby Fischer.