Joe Kelly and Walter McDaniel’s “epic” Deadpool story is really only three issues, with #21 and 22 being prologues to it. This was the story that tried to pull together two years of Deadpool stories into a thematic closure. Way back in #1, we watched representatives from the intergalactic firm of Landau, Luckman and Lake take an interest in Deadpool as the key to the future of the universe, and a hero who would bring about paradise. This messianic role has been the main source of conflict in the series, as Deadpool struggles between being a killer and a hero.
LL&L have told Deadpool about Mithras, an alien being who will ensure all humanity is finally at peace by taking away their free will. He’s done this before, on other planets..
Naturally, Deadpool’s being an “id-based” chaos creature is the antithesis of Mithras, so it makes sense he’d the hero here.
In Dead Reckoning, Deadpool takes on Captain America himself—in the thrall of Mithras—to save the world. And he does it by kicking Cap in the nuts.
This isn’t the best story from Kelly’s run (because he has some truly stellar work with Deadpool) but it is the character-defining one, at least so far, and it seems to have shaped the character all the way into the present day.