Simplify the following text for a Grade 10 native English-speaking person.
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 .