Short answers, pulled from the story.
Lactantius, full name Lucius Caecilius Firmianus Lactantius, was an early Christian author born around 250 who served as an advisor to the emperor Constantine I and tutor to his son Crispus. Renaissance humanists gave him the title "Christian Cicero" because of his elaborately rhetorical Latin style, and Saint Jerome praised his eloquence as worthy of Cicero himself.
The Institutiones Divinae, written between 303 and 311, was the first systematic exposition of Christian theology in Latin. It was intended to demonstrate the futility of pagan beliefs and establish the reasonableness of Christianity to educated pagan critics.
Constantine appointed Lactantius as Latin tutor to his son Crispus in 309-310, when Crispus was probably between ten and fifteen years old. Lactantius followed Crispus to Trier in 317 when Crispus was made Caesar, and as an advisor to Constantine he helped guide the emperor's early Christian religious policy.
The first printed edition was produced in 1465 by German printers Arnold Pannartz and Konrad Sweynheim at the Abbey of Subiaco in Italy. It was the first dated book printed in Italy and probably the fourth book ever printed there. A copy of this edition sold at auction in 2000 for more than one million dollars.
The Latin poem The Phoenix is widely attributed to Lactantius. It retells the myth of the bird that dies and is reborn, drawn from Egyptian and Arabian traditions, and modern scholars have found literary evidence suggesting the author interpreted the myth as a symbol of resurrection. That poem later became the principal source for the Old English poem known by the same title.
Lactantius had converted to Christianity and resigned his post as official professor of rhetoric at Nicomedia before Diocletian issued his first Edict against the Christians on the 24th of February, 303. He anticipated the purging of Christians from the imperial staff and lived in poverty afterward until Constantine became his patron.