There are obvious reasons that Bismark has been used rather than Hitler. It wouldn't just be Germans you would offend, but pretty much everyone else in the world.
That said, why is Chairman Mao used as the Chinese leader when he also ranks in the top 3 mass murderers alongside Hitler and Uncle Joe? I am sure there are many Chinese civ fans out there who could recommend better leaders.
It's a pity you can't choose the leader for your civ when the game starts.
For example, you could choose India with Ghandi and be a peaceful, commercial civ, or choose India with Porus and be militaristic and aggressive. The possibilities are endless.
You can change the leader names in the editor of course, but the pictures can't be altered, so Napoleon will still be a chick regardless of what you edit.
And yes, Napoleon wasn't French, as has already been pointed out.
This discussion could continue with people pointing out that Cleopatra was Greek (the result of 8 generations of Macedonian inbreeding to be exact) or that Theodora wasn't actually the leader of the Byzantines etc...
