Christos is the non-Greek version of a common Greek

Greek language

Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...

 given name

Given name

A given name, in Western contexts often referred to as a first name, is a personal name that specifies and differentiates between members of a group of individuals, especially in a family, all of whose members usually share the same family name...

 which is spelled in two ways:

• "Χρίστος", Chrístos, from the adjective "χριστός", christós, i.e., "anointed" (or "chosen one" as is the Christian theological term for the Messiah
  Messiah
  A messiah is a redeemer figure expected or foretold in one form or another by a religion. Slightly more widely, a messiah is any redeemer figure. Messianic beliefs or theories generally relate to eschatological improvement of the state of humanity or the world, in other words the World to...
  
  ), and
• "Χρήστος", Chrēstos, from the adjective "χρηστός", chrēstós, i.e., "useful".

In Modern Greek both spellings are practically interchangeable and are pronounced the same (with the stress on the penultimate syllable), but differently from Christós, Christ

Christ

Christ is the English term for the Greek meaning "the anointed one". It is a translation of the Hebrew , usually transliterated into English as Messiah or Mashiach...

, which is accented on the last syllable. This eliminates confusion as to whether someone refers to a regular person or to Jesus Christ.
Moving the accent of a word to create a personal name can be observed in other cases as well, e.g. "Σταύρος" (Stávros), from "σταυρός" (stavrós, cross).