There. Concise little wack theory there in the title, yet very plausible. Listen
1) Thomas started it all with his explosive anti-religious anti-establishment text on self-seeking and liberation, free from any and all bounds
2) Marcion hijacked that text and composed a narrative around it, putting its content into his context
3) The canonicals hijacked Marcin and affixed it to Judaism and that's how Christianity came into being
I'm being awfully concise but you'll read more about that in the coming years, by an increasing amounf of various authors from various "bloodgroups" so to say - and if you don't well then I was wrong and you may rub that in whenever you please
If - and only if - Marcion started the death of Jesus (in whatever way possilbe), then I surmise that he introduced Judas as the traitor, and (proto-)Mark is his usually feeble, reluctant witness to that:
Mark 3:16 Simon (to whom he gave the name Peter); 17 James the son of Zebedee; and John, the brother of James, (whom he called Boanerges, which means, Sons of Thunder); 18 Andrew; Philip; Bartholomew; Matthew; Thomas; James, the son of Alphaeus; Thaddaeus; Simon the Zealot; 19 and Judas Iscariot, who also betrayed him. Then he came into a house.
Mark names the disciples for the very first time and starts off with Simon, elaborating on his other name Peter and reserving one entire sentence and verse for him; then the next 10 disciples including Thomas are named in two verses and Judas has his own sentence and verse just like Simon. Why does Judas betray Jesus?
Mark 14:10 Judas Iscariot, who was one of the twelve, went away to the chief priests, that he might deliver him to them. 11 They, when they heard it, were glad, and promised to give him money. He sought how he might conveniently deliver him.
Money - but that's not his motive, certainly not a quantifiable one in Mark's case. Mark leaves a lot of loose ends, probably most if not all unintentional, and this may be one of them: the chief priests promise Judas money in return, but Judas doesn't ask for it; he betrays Jesus out of the blue. He doesn't think of money when going to the priests, he doesn't bring it up before talking to them, and the money is entirely the initiative of the priests. There is no enmity between Jesus and Judas, no scenes, no nothing - there certainly isn't the motive of money for betraying him.
Mark 14:43 And immediately while yet He is speaking, Judas, one of the Twelve, comes up, and with Him a crowd with swords and clubs, from the chief priests and the scribes and the elders. 44 And the one delivering Him up had given to them a sign, saying: “Whomever I shall kiss is He; seize Him and lead Him away securely.” 45 And having arrived, having come up to Him immediately, he says, “Rabbi!” And he kissed Him.
But where does that kiss come from, is that Marcion? Or are 44 and 45 added by Mark?
We can only answer that question when we find out what the kiss represents, and I think that I have done so:
Samuel 20:9 Joab said to Amasa, "Is it well with you, my brother?" Joab took Amasa by the beard with his right hand to kiss him. 10 But Amasa took no heed to the sword that was in Joab's hand. So he struck him with it in the body, and shed out his bowels to the ground, and didn't strike him again; and he died. Joab and Abishai his brother pursued Sheba the son of Bichri.
Now that is quite a scene - isn't it? Impressive, extreme, vile; so utterly ugly that it is almost beautiful, in a sense - beautifully ugly. Joab certainly is not a nobody, he is a son of the sister of David. When Joab's brother gets killed in a fair fight, Joab murders his killer while pretending to want a quiet chat with him, against the wish of David. Against the wish of David, Joab kills David's son Absalom: Absalom gets stuck with his head in a tree, and is hanging there defenceless; Joab thrusts three darts in his heart, just like that. When David replaces Joab as commander of his troops with Amasa, Joab kills him - this is that very scene right here. When David is to be followed up by his son and promised king Solomon, Joab sides with his eldest brother in stead. Joab is the prototype of the betrayer, and a vicious and vile killer at that.
And that is the pointer to Judas, when he kisses Jesus: he personifies Joab, the traitor of traitors. Vicious, vile and ruthless. There are 36 verses in the Tanakh where a kiss is mentioned, and usually there is weeping and embracing going along with it, next to blessing. There is only one violent scene with a kiss in it, and this is it: the utmost despicable act of Joab, traitor of all traitors
If my theory is right, then this is overwhelmingly Tanakh material, solely "property of" the canonicals, and certainly not Marcion's. But the canonicals were discrediting Marcion, not Thomas, and they wouldn't have a motive for picking on Judas / Thomas. So I think it went the usual way: they liked the traitor part, it dind't mean much if anything to them, and they just slapped on Scripture "in order to make it work (even better)": the morsel, the kiss - that's all they needed to add.
Then after that, after Mark, again, history has been written and it can't be undone; it's very much like the baptism of Jesus (oh and how much doth protest Matthew and John), like the abolishing of food laws (fixed by Matthew by committing blasphemy) - but it's there now, chiselled into rock, and they just have to deal with it - and again we see great wiggling of asses, enormous variation here and there, and of course Luke is scared shitless!
His audience will immediately recognise "Judas" for what he is meant to be - so he invents the Satanic possession because all of us are free from blame when we do things while possessed by Satan. I tried that trick once after a wild night out in town but no one would fall for it, alas (I'm just kidding).
And Matthew doesn't give a damn about Judas so he makes it even worse, slaps on even more Scripture, and "has a ball", as they say.
And John? I'm still mulling on the duality of John, who takes away any and all blame and blemish from Judas, turning him into a peace-loving hugger-of-man, who doesn't have a motive, doesn't even kiss Jesus, and is merely an innocent puppet in the hands of Jesus who willingly, knowingly, and purposely drives every single aspect of his Satanic possession - only to dump it all on Thomas! Poor Thomas, who gets used as a stage prop in the final scene where Simon - of all people!!! - gets the prize, with the beloved disciple as the silent witness. Thomas, whose only purpose it is to name-drop the word 'nails' for the first and only time in all the four gospels - Θωμᾶς ὁ λεγόμενος Δίδυμος; was there ever a harder pointer than that?!
Then there also is Thomas who wants to die with Jesus, and Thomas who doesn't know the way - those two little hints can only point to the author of the text, and they're not really that vile, just attesting to his failure to understand, they're actually turning him into one of his own disciples in his own text.
Yet the first two scenes - that's not John, there's clearly a Churchian hand behind it
There - and that's why Judas has the rollercoaster ride that he does have, and the only people that care about him are Luke and John; Luke, who is intended to serve the Marcionite / Thomasine audience, and John, who is somewhat of a fusion between Thomas and the Jesus of the canonicals.
Was Judas an afterthought? He was absolutely irrelevant in Mark, anyone could have played his part