Hitler.

His foolish war not only destroyed Germany but permanently delegitimized right wing views and opened the road for liberal takeover of the west.

The war might've still been won had Hitler not tried to micromanage and cause a series of blunders.

Going to Kiev instead of Moscow in autumn 1941, not stopping before Moscow and digging in when winter had come, firing the professional old guard of the general staff after 1941, diverting army group B to Stalingrad, launching the suicidal Kursk offensive, firing Manstein, giving HIMLER command of the army, not negotiating a separate peace with the Soviets.... the list goes on.

I'll admit that the regime as a whole made a serious mistake by not launching total mobilization in 1940 or 1941, they only began in 1943 when the war was already lost.

The war never had to happen. He didn't need to invade Poland for Danzig. He could've simply bided his time, build up German forces and industry, built up and incorporate Romania, Hungary and the Balkans into his German sphere and wait for Britain to lose its Empire. Ideally, financing independence movements in the British colonies.

Instead he launched a suicidal war that lead to the occupation of Europe by American and Soviet forces.

Yes, he was a great leader and a true patriot. But he was a man who grasped beyond his abilities. He was a enlisted soldier who tried to act like a Field marshal, and failed. His failure not only lead to the destruction of Germany, but the potential death of Western civilization.

Hitler's life is an example of how importance class is. His blunder is what happens when the reins of power are taken by the working class, rather than the well bred middle and upper classes. In a weird way, the nazi revolution was the word's first working class revolution.