Arthur Seyss-Inquart (1892-1946) was an Austrian lawyer who was active in pan-German nationalism, but did not become a Nazi until 1932.  He was involved in the 1938 Anschluss, and then became a Nazi official in the occupations of Poland and the Netherlands. Especially for the occupations, in which he was deeply involved in deportations, he was convicted of crimes against humanity by the Trial of the Major War Criminals and executed.
He was born in Stannern, Austria, and served in the Austro-Hungarian Army in World War I, receiving severe wounds and being decorated for bravery. Invokved in right-wing politics in Austria, he became a state counselor in 1937, and Reich Governor of Austria in 1938. He then became deputy to Hans Frank as head of the Generalgouvernement occupation administration in Poland.
Airey Neave, in his memoir of representing the Nuremberg prosecution to the defendants, found him puzzling, as "decorous and inscrutable", and resigned to his fate. He mentions that some considered him a pan-German nationalist, and others thought him a traitor to his country. Neave wrote that "nothing he did in 1938 or after the Anscluss as Reich Governor of Vienna would have earned him the death sentence," those sentences being based on Poland and the Netherlands. Neave said he had a fanatical obsession with race. 
His tenure in Poland was short. Neave thought him proud of his honorary SS rank, and at least a silent partner in atrocities.
Next, he was Reich Commissioner for the Netherlands until the end of the war, and was judged responsible for shooting of hostages and deportation of Jews. The Tribunal judgment called him "ruthless in using terrorism to suppress all opposition to the German occupation, a programme which he described as " annihilating " his opponents. In collaboration with the local Hitler SS and Police Leaders he was involved in the shooting of hostages for offences against the occupation authorities and sending to concentration camps all suspected opponents of occupation policies including priests and educators. Many of the Dutch police were forced to participate in these programmes by threats of reprisal against their families. Dutch courts were also forced to participate in his programme, but when they indicated their reluctance to give sentences of imprisonment because so many prisoners were in fact killed, a greater emphasis was placed on the use of summary police courts."
The Tribunal acknowledged "it is true that some of the excesses were the responsibility of the Army, and that the Higher SS and Police Leader, although he was at the disposal of Seyss-Inquart, could always report directly to Himmler. It is also true that in certain cases Seyss-Inquart opposed the extreme measures used by these other agencies, as when he was largely successful in preventing the Army from carrying out a scorched earth policy, and urged the Higher SS and Police Leaders to reduce the number of hostages to be shot. But the fact remains that Seyss-Inquart was a knowing and voluntary participant in war crimes and crimes against humanity which were committed in the occupation of the Netherlands." He was named the final Reich Foreign Minister in Hitler's political testament. Some of his acts to prevent scorched-earth tactics were in cooperation with Albert Speer. Speer wrote that the two of them shared some understanding of the principle of responsibility. His last words were
I hope this execution is the last act of the tragedy of the Second World War and I hope, out of this disaster, wisdom will inspire the people, which will result on understanding between the nations and peace on earth will finally be established.
- Airey Neave (1978), On Trial at Nuremberg, Little, Brown, pp. 164-165
- Neave, pp. 163-165
- Judgment of Seyss-Inquart, Trial of the Major War Criminals, International Military Tribunal
- Albert Speer (1970), Inside the Third Reich, Macmillan, p. 511
- Neave, pp. 317-318