There are several theories of his available online for perusal. For example, he has famously argued that Simon Magus was a/the main point of origin for the Christian religion (part 1, part 2, part 3, part 4, part 5, part 6, part 7, part 8, part 9, part 10, part 11, part 12, part 13, part 14, part 15, part 16, part 17). As another example, he has also argued that both the Ignatian epistles and the Johannine gospel are products of an Apellean branch of Christianity. Most recently, he has revised his Simonian theory considerably (part 1, part 2, part 3, part 4), and has wound up suggesting in the process that Paul's epistles have gone through a stage of revision and interpolation at the hands of somebody in the Saturnilian camp.
What all of these theories have in common is that they all attempt to actually name the person (Simon Magus, Apelles, Saturnilus/Saturninus) or the group (Simonians, Apelleans, Saturnilians/Saturninians) responsible for an important early thrust in Christian development. Moreover, they do so without constantly coming back to the same tradent (Marcion!), which is a trap into which many researchers have fallen. It is possible that Parvus is completely mistaken in his identifications, but I think that the attempt is very much a worthy one. There are almost certainly individuals and groups in early Christianity whose names have completely disappeared from the historical record, but who nevertheless made important contributions along the way (and this disappearing act was probably even more severe for Jewish groups, due to the disruption and upheaval provided by the fall of the Jewish homeland, than for gentile groups); but, before simply inventing such an individual or group to shoulder the burden of our hypotheses, perhaps it would repay our attention to try to find one from among the names that we do possess.
The contrast is very keen, for example, in the matter of whether 1 Corinthians 2.6-16 might not be an interpolation. William O. Walker argues that it is, but, when the time comes to identify who might have been responsible for its insertion into the epistle, he has only this to say:
The culprit is just "someone" who wanted to ensure that Paul was counted among "the spiritual ones." There is nothing wrong with this, but consider that, when the time comes for Roger Parvus to identify the party responsible for penning 1 Corinthians 2.6-9, he names Saturnilus or one of his followers. I love that he has sifted through the various early "heresies" (as identified by the heresiologists) for possible suspects, just as he did for Simon and for Apelles. Even if we can never be sure that it was precisely Saturnilus/Saturninus, to take the case in point, or one of his followers who interpolated something into a Pauline epistle, it helps to be aware that it may well have been somebody who thought in much the same way as he did. (I also find it interesting that Parvus has identified, not only 1 Corinthians 2.6-9, but also Philippians 2.5-11 as part of a secondary layer in the Pauline epistles. I have been slowly thinking along the same lines myself with respect to both passages, which seem closer in spirit to some of the deutero-Paulines than to the Pauline stuff that I think I can demonstrate to be earlier and probably primary. He also places 2 Corinthians 12.1-10 in this same category, but I admit I have given next to zero thought to that topic as of yet.)
I post this by way of reminder to myself no less than to anyone else, as I have invented possibly more than my fair share of early tradents in the course of theorizing about the development of the Christian faith. Some of those inventions still feel justifiable to me; others perhaps not so much. It is not as if I have never explored the strata of various early "heresies" from which Parvus mines his suspects (I have posted before about the Quartodecimans and the Nicolaitans, and I have files on my hard drive in which I have been collecting data about Valentinus, Basilides, and a few other figures); but I am not always thinking of any of those tradents when I propose some early development in Christianity, and maybe I ought to be.
Another reminder from Parvus, seemingly unwittingly on his part, is the necessity of questioning one's own assumptions and, if necessary, changing one's mind. His most recent series of posts on Vridar is quite a thoroughgoing modification of his previously posted Simonian theory (in four parts, links to which are posted above). At any rate, if you like to read Roger Parvus with anything approaching my own enthusiasm, I definitely recommend this most recent series of his.
Ben.