Who Was the Marcionite Apostle?

It's a very interesting question and it one that arises out of several works directly or indirectly attributable to Irenaeus.  The idea that the heretics 'kept silent' about the identity of their apostle is repeatedly referenced in his writings including:

Moreover we must not keep silence respecting Paul, but demand from them after the type of what AEon that apostle has been handed down to us, unless perchance of the Saviour compounded of them, who derived his being from the collected gifts of the whole, and whom they term All Things, as having been formed out of them all. [AH 2.21.2]

Wretched men indeed! who wish to be pseudo-prophets, forsooth, but who set aside the gift of prophecy from the Church; acting like those who, on account of such as come in hypocrisy, hold themselves aloof from the communion of the brethren. We must conclude, moreover, that these men can not admit the Apostle Paul either (neque Apostolum Paulum recipiant). [ibid 3.11.9]

But again, we allege the same against those who do not know the apostle Paul (qui Paulum Apostolum non cognoscunt) that they should either reject the other words of the Gospel which we have come to know through Luke alone, and not make use of them; or else, if they do receive all these, they must necessarily admit also that testimony concerning Paul, when he (Luke) tells us that the Lord spoke at first to him from heaven: "Saul, Saul, why persecutest thou Me? I am Jesus Christ, whom thou persecutest"  Those, therefore, who do not accept of him, who was chosen by God for this purpose (qui igitur non recipiunt euni qui sit electus a Deo ad hoc), that he might boldly bear His name, as being sent to the forementioned nations, do despise the election of God, and separate themselves from the company of the apostles (et se ipsos segregant ab apostolorum conventu). For neither can they contend that Paul was not an apostle (neque enim contendere possunt Paulum non esse Apostolum), when he was chosen for this purpose; nor can they prove Luke guilty of lying (neque Lucam mendacem esse possunt ostendere), when he proclaims the truth to us with all diligence. It may be, indeed, that it was with this view that God set forth very many Gospel truths, through Luke's instrumentality, which all should esteem it necessary to use, in order that all persons, following his subsequent testimony, which treats upon the acts and the doctrine of the apostles, and holding the unadulterated rule of truth, may be saved. His testimony, therefore, is true, and the doctrine of the apostles is open and stedfast, holding nothing in reserve; nor did they teach one set of doctrines in private, and another in public.[ibid 3.15.1]

They allege that in separating the Law and the Gospel Marcion did not so much invent a new rule as refurbish a rule previously debased. So then Christ, our most patient Lord, has through all these years borne with a perversion of the preaching about himself, until, if you please, Marcion should come to his rescue.[Tertullian Against Marcion 1.20] 

As corrector apparently of a gospel which from the times of Tiberius to those of Antoninus had suffered subversion, Marcion comes to light, first and alone, after Christ had waited for him all that time, repenting of having been in a hurry to send forth apostles without Marcion to protect them. And yet heresy, which is always in this manner correcting the gospels, and so corrupting them, is the effect of human temerity, not of divine authority: for even if Marcion were a disciple, he is not above his master: and if Marcion were an apostle, Whether it were I, says Paul, or they, so we preach and if Marcion were a prophet, even the spirits of the prophets have to be subject to the prophets, for they are not of subversion but of peace: even if Marcion were an angel, he is more likely to be called anathema than gospel-maker, seeing he has preached a different gospel. [ibid 4.5] 

It is, I suppose, on these considerations, Marcion, that you have presumed to delete all those documents bearing on Christ's origins, to prevent his flesh being proved to be flesh. On whose authority, pray? Show your credentials. If you are a prophet, foretell something: if an apostle, preach publicly: if an apostolic man, agree with the apostles: if but an ordinary Christian, believe the traditional faith. If you are none of these--I have good reason for saying it--die. Nay, you are already dead, for you are not a Christian, seeing you do not believe that which, when believed, makes men Christians: and you are the more dead as you are the more not a Christian as having been one and having fallen away by annulling what you formerly believed, as you yourself claim in a certain epistle, and as your people do not deny, and ours prove [On the Flesh of Christ 2]

It is quite another thing if he made a pretence of choosing them from the Association of Shipmasters, because he was sometime going to have as his apostle Marcion the navigator. [ibid 4.9]

But if you refuse acknowledgement of John, you have a common teacher Paul (habes communem magistrum Paulum), who girds our loins with truth, and with the corselet of righteousness, and shoes our feet with the preparation of the gospel of peace [Tertullian Against Marcion 3.14]

Now Luke was not an apostle but an apostolic man, not a master but a disciple, in any case less than his master, and assuredly even more of lesser account as being the follower of a later apostle, Paul, to be sure: so that even if Marcion had introduced his gospel under the name of Paul in person, that one single document would not be adequate for our faith, if destitute of the support of his predecessors. For we should demand the production of that gospel also which Paul found , that to which he gave his assent, that with which shortly afterwards he was anxious that his own should agree [ibid 4.3]

But, you know, your own apostle does not permit the members of Christ to be joined to a harlot.[ibid 4.34]

I desire to hear from Marcion the origin of Paul the apostle ... I must with the best of reasons approach this inquiry with uneasiness when I find one affirmed to be an apostle, of whom in the list of the apostles in the gospel I find no trace. So when I am told that he was subsequently promoted by our Lord, by now at rest in heaven, I find some lack of foresight in the fact that Christ did not know beforehand that he would have need of him, but after setting in order the office of apostleship and sending them out upon their duties, considered it necessary, on an impulse and not by deliberation, to add another, by compulsion so to speak and not by design. So then, shipmaster out of Pontus ... will you please tell us under what bill of lading you accepted Paul as apostle, who had stamped him with that mark of distinction, who commended him to you, and who put him in your charge? Only so may you with confidence disembark him: only so can he avoid being proved to belong to him who has put in evidence all the documents that attest his apostleship. He himself, says he, claims to be an apostle, and that not from men nor through any man, but through Jesus Christ. [ibid 5.1]

Now here I may say to those who reject the Acts of the Apostles: "The first thing for you to do is to shew who this Paul was—both what he was before he was an Apostle, and how he became an Apostle".; since at other times they make very great use of him in disputed matters. For though he himself declares that from a persecutor he became an Apostle, that statement is not sufficient for one who yields credence only after proof. For not even the Lord Himself bore witness concerning Himself. But let them believe without the Scriptures that they may believe against the Scriptures. [Tertullian Prescription 23]

No man is for himself both claimant and witness. Besides this, you have found it written that many will come and say, I am Christ. If there is one that makes a false claim to be Christ, much more can there be one who professes that he is an apostle of Christ. Thus far my converse has been in the guise of a disciple and an inquirer: from now on I propose to shatter your confidence, for you have no means of proving its validity, and to shame your presumption, since you make claims but reject the means of establishing them. Let Christ, let the apostle, belong to your other god: yet you have no proof of it except from the Creator's archives. [ibid] 

From them I prove that the persecutor became an apostle, not from men, nor by a man: from them I am led even to believe him: by their means I dis- lodge you from your claim to him, and have no fear of you when you ask, And do you then deny that Paul is an apostle? I speak no evil against him whom I retain for myself ... So then accept the apostle on my evidence, as as you do Christ: he is my apostle, as also Christ is mine.[ibid 5.2] 

For of Israel he says, Until this very day the same veil is in their heart. He indicates that the veil of the face in Moses was a figure of the veil of the heart in that people, because among them even now Moses is not clearly seen with the heart, just as then he was not clearly seen by face. What then is there still under a veil in Moses that has reference to Paul, if (as you allege) the Creator's Christ prophesied by Moses has not yet come? [ibid 5.11] 

Hence arise certain persons' over-precise or even audacious discussions as to how, in view of that standing rule, the apostles can have obtained salvation, when we observe that none of them except Paul were baptized in our Lord: in fact, since Paul is the only one from among them who has put on the baptism of Christ [On Baptism 12]