Why was Santiago called El Campeon in The Old Man and the Sea?

This section of the novel comes as the sun sets one evening on
Santiago as he is out in the sea and he remembers a time when he was victorious "to give himself
more confidence." He remembers when he was playing the hand game with a black man called
Cienfuegos (a hundred fires). The battle raged back and forth all night, but in those days we are
told that just as this man had his nickname, Santiago was called El Campeon (the
champion):

The odds
would change back and forth all night and they fed the negro rum and lighted cigarettes for him.
Then the negro, after the rum, would try for a tremendous effort and once he had the old man, who
was not the old man then but was Santiago El Campeon, nearly three inches off
balance.

Thus Santiago is remembering
another titanic struggle to recall his strength and powers of perseverance. Although he only
possessed this nickname when he was young, it speaks a lot about the depths of his strength and
stubborness: precisely the qualities that he has to resurrect to catch the fish he is now engaged
in a conflict with.