heaven-3
Explanation
The Joke
The comic shows a single-panel scene at the gates of heaven. A figure shown in silhouette stands before Saint Peter (or God) at a podium, indignantly protesting: "What do you mean I don't get in?! I killed Hitler!" The caption below reads: "Hitler fails to enter Heaven."
The joke is a logical paradox: Hitler killed himself (he committed suicide in his bunker in April 1945), so technically he is "the person who killed Hitler." He is attempting to use this fact as a moral credential to gain entry into heaven, arguing that killing one of history's greatest monsters should earn him admission. Of course, the reason he was able to "kill Hitler" is that he IS Hitler, which is also the reason he is being denied entry.
The Humor
The humor operates as a classic logic puzzle punchline. The reader initially sees the silhouetted figure and the claim "I killed Hitler" and might momentarily wonder who this could be -- a time traveler? An assassin? The caption then delivers the devastating reveal that the speaker is Hitler himself, exploiting a technicality about his own suicide. The joke works because the statement "I killed Hitler" is technically, literally true, while being the most disingenuous possible framing of what actually happened. It is also funny that Hitler apparently thought this argument would work on an omniscient deity.
References
Adolf Hitler died by suicide on April 30, 1945, in his underground bunker (the Fuhrerbunker) in Berlin as Soviet forces closed in on the city. This historical fact is the basis for the joke's wordplay.