The Apologists were Christian writer of the first two Christian centuries who's defended Christianity as well as helped define it in an academic sense. In this context an apology means a formal justification or defense of an idea. The Apologists were often answering a specific challenge to Christianity and their writings do not produce what we would today call a systematic theology. In their defense of a particular idea they were often focused on the issue at hand.

In the face of criticism from Greek philosophers and facing persecution from the Jewish authorities, the Apologetic Fathers wrote to justify and defend the Christian faith and doctrine. The Apologists were the first writers to frame an intellectually satisfying explanation of the relationship of Christ to God the Father. "They were all monotheists determined at all costs not to compromise this point. The problem being 'what does it mean for God to have a Son?' (Kelly 1978 p 95)"

We can see that the apostles, in New Testament times, were engaged in this sort of exercise as well with the Jews and the Greeks. We see that Paul goes first to the synagogues in his travels reasoning from the scriptures, which would be our Old Testament. He also goes to the Greeks, confronting them with philosophy and on the basis of their own belief in gods (Acts 17).

Important Apologists.
Date Apologist
c. 117 - 138  Quadratus of Athens
c. 80 - 140 Aristides 
c. 3rd century Hermias
c. 2nd century Apollinaris of Hierapolis
110 - 165 Justin Martyr
d 185 Tatian 
120 - 190 Athenagoras of Athens
c. 155 - 230 Tertullian