Eusebius

 Have you ever heard of Eusebius?  I never did, much to my shame.  He's pretty important--very much so.  He was a theologian, historian, and apologist.  Seeing his father martyred for Christianity, around the turn of the century, cemented his resolve to remain Christian and spread the faith.  

Once Constantine legalized Christianity, many people became Christians for weak reasons.  All sorts of strange ideas about what Christianity had arisen.  The Nicaean creed should have been followed but others, Arians during Eusebius' time, especially, argued their views. True Christianity was attacked.  The Arians harassed Eusebius, put him in prison, and beat him. He was steadfast.

He wrote Ecclesiastical History, which prescinded Acts of the Apostles and is considered the first history of the church.  It was a different genre, for the times, which were works of classical Greek and Latin historiography.  This history provided the inspiration for all the church historians writing up to the invasion of the barbarian tribes, in the first three centuries.