'.
'Foremost' shows 'the most notable'.
The correct sentence should be: It is a fact that John F. Kennedy was the 
 politician of his time.
| He is the foremost dancer of our time. | 
| She was the foremost leader of her time. | 
| First in beauty is first in might. | 
| The first edition was published in the year 1995. | 
 First and foremost can be used together in a sentence, when the idea in the sentence is to be intensified.
e.g. Our 
 duty is to protect our motherland.