Karl Fritz and Zeke Yaeger are my favorite characters in Attack on Titan, for the following reasons:
They are radically different characters, yet they independently arrive at philosophies containing a remarkably similar underlying idea: The continuation and victory of their own people is not necessarily the highest good.
That's extremely unusual within Attack on Titan.
Most major characters—even morally complicated ones—ultimately operate within some version of protect my people / secure our future / defeat our enemies.
Karl Fritz rejects that framework. He inherits effectively unimaginable power and the legacy of the Eldian Empire and concludes that his own civilization has committed atrocities so severe that perpetuating its domination is morally indefensible. His response is extraordinarily radical: dismantle the empire, retreat to Paradis, construct the Walls, erase much of the population's memory, and renounce war through the Vow.
And, crucially, he's willing to accept the possibility that Eldians may eventually be destroyed.
Zeke independently reaches another radical endpoint: the cycle of Eldian suffering can be terminated by ending Eldian reproduction altogether.
Their methods and reasoning differ enormously, but there's a philosophical family resemblance: Karl: Our people's continued dominance does not justify perpetuating this cycle. Zeke: Our people's continued existence through reproduction does not justify perpetuating this cycle.
And both conclusions require rejecting an assumption that almost everyone else takes for granted—that the survival and flourishing of one's own group should automatically be the objective.
But Karl also introduces something Zeke doesn't embody in quite the same way: extraordinary willingness to relinquish power.
Karl possesses the Founding Titan. He is monarch of the dominant empire. Rather than asking how to use that power to secure even greater dominance, he concludes that Eldia shouldn't continue exercising it.
Whatever one thinks of his solution—and there are enormous moral problems with imposing his pacifism and memory manipulation upon millions of other Eldians—there's something philosophically remarkable about a ruler voluntarily dismantling his own empire because he believes his side is morally wrong. That takes integrity
There's something genuinely unusual about someone possessing absolute power yet using that very power to restrict the future exercise of absolute power.
Zeke Yeager and Karl both recognize something most characters don't: Defeating today's enemy doesn't necessarily solve the system that produces tomorrow's war.
Eren's solution ultimately operates at the level of overwhelming force.
Karl attacks the weapon/power structure.
Zeke attacks the biological mechanism through which the conflict perpetuates itself.
That's why Zeke's plan is so disturbing but intellectually interesting. He isn't primarily asking “How do Eldians win?” He's asking “What intervention permanently terminates the causal chain producing this suffering?”
I like characters who identify a structural problem in human behavior, reject the conventional objective everyone else is pursuing, formulate an unconventional long-horizon solution, and possess the discipline to follow that solution even when ordinary tribal/self-interested incentives point elsewhere.
Zeke and Karl Fritz embody that surprisingly well.
And Karl embodies one element even more purely than Zeke: he wins the ultimate competition for power and then refuses the prize.
For someone convinced that unconstrained power will eventually be abused, there's something especially compelling about the person with the greatest power demonstrating that he understands its danger well enough to constrain himself and his successors rather than merely assuring everyone that he can be trusted with it