How to use 者 as "... one who is ..."?
者
  
  英文翻譯: that which; he who; those who
  
  《禮記·檀弓上》
  遂命子貢為之主，曰：「為爾哭也來者，拜之。」
  
  Accordingly he ordered Zi-gong to act as presiding mourner on the occasion, saying to him, 'Bow to those who come because you have a wailing in your house.'


之 in 拜之 is a pronoun which represents 來者.

I think it is usually used in the classical Chinese (文言文).