What happened during the finale was kinda hard to truly analyze because so many things occured at once. But one thing seriously bugged me.

If the finite curve is...well finite and there's only so many Smartest Ricks in the universe...why didnt C-137 found the "Killer Rick" ? He spent 20 years and killed thousands, if not milions of Ricks throught that time. (thats how im gonna call the Rick that killed C-137's wife, for simplicity's sake.)

It might seem like E.Morty implies that our Rick created it, but in reality he doesnt do that. He only knows that C-137 knows how to break through it. "How the fuck E.Morty knew that this Rick specifically knows how to break it" is a whole another topic for another theory, so lets focus on the main part that supports this idea i just presented.

You see the portal colors are extremely consistent since Season 3, no matter what. The Blue portals are used for travel from one point in current reality to another point in current reality. (Rick's backstory, President's portal.) The Green portals however were revealed to teleport things WITHIN the finite curve itself. thats how Our Rick could travel throught his whole life. And now the golden portals are highly likely to teleport stuff between realities without any limitations. Anything goes with these.

And im mentioning this because in Rick's backstory, Killer Rick opens a GREEN PORTAL. this directly implies that THE FINITE CURVE EXISTED BEFORE C-137 CREATED HIS PORTAL GUN, WHICH WAS ALSO GREEN. This is exactly why its impossible for our Rick to create that curve, because the sole reason why his family got killed is that he was one of the "Smartest Ricks in the universe" . Thats why Killer Rick paid him a visit.

Now this is the main meat of my theory that states the following : Killer Rick left the finite curve a long time ago. and he was the one that created it.

The reasons why are kinda impossible to guess right now, but he did definetly left the curve, and thats exactly why our Rick could have never find him after looking for so long and killing so many Ricks in the process. Its all connecting to one thing : C-137 is the Rickest Rick of them all.

Why is he the Rickest Rick of them all? because out of all of these smartest ricks, he is the one that figured out HOW to break through the finite curve. HOW TO BREAK THE CYCLE. and this is his personal reason as to why he helped Ricks that he kept killing create the citadel. To use its residents the same way Evil Morty did to break from the finite curve himself.

And now that the finite curve was crossed and possibly destroyed, its why we visibly see all the portal fluid of the finite curve evaporating, essentially making dimensional travel impossible for our Rick and Morty untill they possibly get the golden fluid. It might seem like E.Morty just simply crossed it but i heavily doubt that. Rick looks concerned that even the fluid in his portal gun completly evaporated, while E.Morty looks at the "finite curve map" and watches it crumble apart, before using a golden portal gun to teleport away, not a green one. Symbolising that the finite curve ceased to exist. This event might draw the attention of...yep. Killer Rick.

So thats the theory. What do you think?

and here's a few more things to add here for clarity that i didnt know where to fit in this theory : Morty just became a new constant of the finite curve itself as the time progressed through. Before Citadel's mania to create infinite grandsons, the finite curve's main reason to exist was to collect Ricks that are the smartest beings in their own respective realities. after Killer Rick left for whatever reasons, The era of the Citadel started and thats when Morties were mass produced for, again, Rickest Rick's finite curve breakthrough plan.

Whatever Morty learned when seeing Rick's backstory is definetly not his full backstory, as we still dont know whats the deal with baby morty in his memories, among other things.

His master plan was either discovered by the citadel and he was kicked out of it, Or something else happened that we dont know yet that made Rick abandon his quest for revenge and crash the ship in Beth's garage.