Short answer. Valentinus (c. 100-160 CE) was an Egyptian-born, Alexandrian-educated Christian teacher who worked in Rome for roughly two decades in the mid-second century and became the most influential of the teachers now labeled Gnostic. Tertullian, a hostile witness writing decades later, reports that he was a serious candidate for bishop of Rome and broke away when passed over. The elaborate system that carries his name (the Pleroma of aeons, the fall of Sophia, the demiurge) is reported mainly by his opponents, and how much of it goes back to Valentinus himself is one of the live debates in the field.
An Alexandrian in Rome
Almost everything we know about Valentinus the man comes from his enemies, which is the first fact to hold onto. Epiphanius, writing around 375 and admitting he worked from hearsay, says Valentinus was born on the Egyptian coast and educated in Alexandria (Epiphanius, Panarion 31), the intellectual capital of the Mediterranean and home to the allegorical reading of scripture his work everywhere presumes. The firmer datum comes from Irenaeus, writing within living memory: Valentinus "came to Rome in the time of Hyginus, flourished under Pius, and remained until Anicetus" (Irenaeus, Against Heresies 3.4.3), which puts him in the capital from roughly 136 to about 160. What survives in his own voice is a handful of fragments quoted by Clement of Alexandria in the Stromateis and by Hippolytus: pieces of letters, homilies, and a striking psalm on the chain of being (Refutation of All Heresies 6.37). Read on their own, the fragments show a lyrical, Platonizing Christian preacher, closer to a poet than to the system-builder his opponents describe.
Did he really almost become bishop of Rome?
The famous story comes from a single hostile source. Tertullian, writing around half a century after the events, says Valentinus "expected to become a bishop, because he was an able man both in genius and eloquence," but that another man "obtained the dignity by reason of a claim which confessorship had given him" (he had suffered for the faith), and that Valentinus, indignant, broke with the church (Tertullian, Against the Valentinians 4). Flag this hard: it is reported only by an adversary, it fits a stock polemical script in which heresy is born of thwarted ambition rather than conviction, and Irenaeus, who wrote earlier and knew the Roman scene better, says nothing about any candidacy. Tertullian elsewhere gives a partly conflicting account of Valentinus's break with the Roman church (Prescription Against Heretics 30). So the episode cannot be treated as settled fact. What it does show, even if embellished, is what the slander needed to be plausible: Valentinus was prominent enough in mid-century Roman Christianity that a near-miss at its highest office made a believable story. He was no marginal crank.
What was the Valentinian system?
The full mythology is reported by Irenaeus (Against Heresies 1.1-1.8). In it, the ultimate God is an unknowable Depth (Bythos) who, with Silence, emanates a Fullness (the Pleroma) of thirty aeons in paired syzygies. The youngest aeon, Sophia (Wisdom), conceives a passion to comprehend the unknowable Father; her crisis ruptures the Pleroma, and from its expelled residue come the material world and its maker, the demiurge, an ignorant craftsman-god who believes himself supreme. Humanity falls into three kinds: the material, the psychic, and the spiritual, who carry a seed of the Pleroma and are destined to return to it. Christ comes to awaken that seed with saving knowledge (gnosis). One caution belongs in the same breath: Irenaeus explicitly says he is describing "the disciples of Ptolemaeus, whose school may be described as a bud from that of Valentinus" (Against Heresies 1, preface). Whether the master taught this myth in this form is a reconstruction, not a settled fact, and the authentic fragments show surprisingly little of it.
Did Valentinus write the Gospel of Truth?
Irenaeus complains that the Valentinians boast a work "which they style the Gospel of Truth" (Against Heresies 3.11.9). Among the Coptic codices found at Nag Hammadi in 1945 is a text (Codex I,3) whose opening words are exactly that: not a narrative gospel but a rhapsodic meditation on error, forgetfulness, and the Father made knowable in Jesus. Many scholars have argued that its style matches the authentic fragments closely enough to suggest Valentinus himself as author, which would make it the only extended work by one of the founding heresiarchs of this era to survive in his own words. But the manuscript names no author, the attribution remains a hypothesis, and the field has not closed the question (Layton, The Gnostic Scriptures, 1987; Thomassen, The Spiritual Seed, 2006). The honest formulation: possibly by Valentinus, certainly from his school, and beautiful either way.
The real threat: they stayed inside
Marcion, Valentinus's contemporary in Rome, split off and built a rival church. The Valentinians did the opposite, and this is precisely what enraged their opponents. Irenaeus complains that they "say the same things, and hold the same doctrine" as other Christians while complaining at being called heretics, "imitating our phraseology" to win a hearing (Against Heresies 3.15.2). Valentinians worshiped alongside ordinary believers, used the same scriptures and much of the same language, and treated common faith as a true but lower rung, with their own teaching as its deeper meaning. A church within the church, invisible from the pews. That is why the heresiologists feared Valentinus more than the open schismatics: you cannot expel what you cannot distinguish. Much of the machinery of emerging orthodoxy (creeds, rules of faith, episcopal authority) was sharpened partly on this problem.
The man versus the ism: where scholarship stands
Modern scholarship has pulled the man and the movement apart. Christoph Markschies (Valentinus Gnosticus?, 1992) argued that the authentic fragments show a Platonizing Christian theologian and rhetor with little trace of the mythological system, so that "Valentinianism" may be largely the work of his students, packaged by his enemies. Einar Thomassen's The Spiritual Seed: The Church of the "Valentinians" (2006), the standard modern study, reconstructs the whole tradition from the Nag Hammadi texts and the patristic reports, distinguishes eastern and western branches of the school, and is more willing to see real continuity between the master and the system. The honest headline is the spread itself: positions run from "Valentinus the Gnostic barely existed" to "the system is substantially his," and this page reports the debate rather than picking a winner (see also Dunderberg, Beyond Gnosticism, 2008).
Common questions
Was Valentinus a Christian?
He certainly considered himself one: he taught inside Christian communities, quoted Christian scripture, and preached Christ as revealer and savior. Whether "Gnosticism" was a separate religion or a current within early Christianity is itself a modern scholarly debate. The most defensible framing is that second-century Christianity was a contest between rival visions of the faith, and Valentinus led one of the most sophisticated. He lost the naming war, so his movement is remembered as a heresy rather than a road not taken.
What did Valentinus actually write?
Securely, only fragments survive: roughly half a dozen quotations from letters and homilies preserved by Clement of Alexandria (Stromateis) and Hippolytus, plus a psalm quoted in Hippolytus's Refutation of All Heresies 6.37. Beyond that, the Gospel of Truth from Nag Hammadi is attributed to him by many scholars on grounds of style, but the attribution is debated and the manuscript itself names no author.
Was Valentinus condemned in his lifetime?
The evidence is late and partisan. Irenaeus, writing around 180, treats him as the fountainhead of error but reports no formal act against him. Tertullian, later still, says he broke with (or was expelled from) the Roman church, in accounts that do not fully agree with each other or with Irenaeus's chronology. The formal machinery of excommunication was itself still taking shape in this period, which is part of why the Valentinians could remain inside congregations for generations.
What happened to the Valentinians after him?
The school outlived its founder by more than two centuries, spreading through teachers like Ptolemy and Heracleon (author of the earliest known commentary on the Gospel of John) and dividing, per the ancient reports, into eastern and western branches (Thomassen, The Spiritual Seed, 2006). Valentinian communities are still attested in the late fourth century, when imperial anti-heresy legislation and episcopal pressure finally pushed them out of existence. The Nag Hammadi find returned several of their texts to daylight in 1945.
This page reports what the ancient sources say about Valentinus and flags which reports come from his enemies; it does not treat the system described by Irenaeus as the master's verbatim teaching, and it does not adjudicate whether his theology was true.
Sources
Irenaeus, Against Heresies (c. 180), esp. 1.1-1.8, 1 preface, 3.4.3, 3.11.9, 3.15.2; Tertullian, Against the Valentinians 4 and Prescription Against Heretics 30; Clement of Alexandria, Stromateis; Hippolytus, Refutation of All Heresies 6.37; Epiphanius, Panarion 31; the Gospel of Truth (Nag Hammadi Codex I,3); Einar Thomassen, The Spiritual Seed: The Church of the "Valentinians" (2006); Christoph Markschies, Valentinus Gnosticus? (1992); Bentley Layton, The Gnostic Scriptures (1987); Ismo Dunderberg, Beyond Gnosticism (2008).