Greek language
Greek is the most ancient continuously written language in human history. It securely dates, as a written language from ca. 800 BC as the language of Homer and continues continuously to the present day, as four to five different languages through time. Homeric Greek, or simply Homeric is the earliest literary language, a form of Attic-Ionic. There is late Archaic Greek, which follows Homeric, and culminates in Classical Greek, with Aeschylus and Sophocles, and then later Classical Greek, with Plato and Aristotle, into the strange plays of Euripides and the obscene plays of Aristophanes.
The Greek spread by Alexander was literary. By the 1st century AD, and with the New Testament, it was koine, 'common' Greek, the sort of Greek that can be compared to well-spoken illegal immigrants from Central American in the United States. Accented, using slang, etc.
Some centuries before, the Jews of Alexandria rendered a version of the Old Testament into Greek. This is is called the Septuagint, the LXX, 'the seventy' (or 'seventy-two' according to some good sources). This version of the Old Testament differs from that used by most Protestants, but continues to be used by the Catholics (in Latin) and by the Greek Orthodox (untranslated). Most Protestants follow Luther in following the Jewish canon.
The early Greek language no longer exists in a spoken form today, modern Greek being as different from Classical Greek as Old English is from current English.
Modern Greek is the modern variety of the Greek language, but separate from ancient Greek. It is the primary language of Greece and Cyprus.