There are over thirty extant treatises by Tertullian (ca.160 – ca. 220). Converted in Rome where he had been sent to study law, he rejected the immorality he found all about him in Rome and returned to Carthage. Unlike Origen, Tertullian believed the book of Hebrews to have been written by Barnabas and not Paul though he felt it should be included in the canon. Tertullian coined the term Trinity in reference to the Godhead postulating that in one substance was three persons.
Most of Christianity today also holds to Tertullian’s view of original sin being transmitted to the successive generations from Adam. This view came from Tertullian’s belief that the soul was actually material and that it was procreated along with the body by a person’s parents. Additionally, it was Tertullian who’s Against Praxeas is famous for affirming that Jesus has two natures joined in one person.  All of these contributions of Tertullian are significant but the historical context in mentioning him is that found in his writings around the turn of the century is the first use of the term New Testament.
Origen (185 – 254) compiled a complete listing of the books of the Old Testament. Unfortunately, the same cannot be said of the New Testament canon. Bruce argues Origen initially had little interest in the question of canonicity of New Testament writings. Later, he would write commentaries on most of the books of the New Testament with a particular focus on inspiration by God. Origen was a prolific writer based on the literal text of Scripture which he held to be accurate historically. His De Principiis, already mentioned earlier, is one of the first attempts at a systematic theology. Perhaps Origen’s most famous work is his Hexapla which was a six-columned Bible with the original Hebrew, a transliterated Greek, the version of Aquila, the version of Symmachus, and the text of the LXX as it existed at that time.
Though Origen wrote at a time before what most Christians consider a correct view of the Trinity became proper doctrine, he did affirm God as the creator of all things, Christ as eternal Son and Word, and the Holy Spirit with each member distinct from the others but forming one. At other times though, Origen would speak of the Son and Holy Spirit as being subject to the father. This view led others to subordination and at times to Arianism. Origen died several years after suffering during the Decian persecution in 254. In 553 he was declared a heretic though in very recent years Origen’s fame has been rehabilitated mostly through efforts to distinguish his doctrines from those attributed to him later by his so-called followers.