Possibly Major General Henning von Tresckow. He didn't shoot himself though, he used a hand grenade to kill himself.
His last words were: "The whole world will vilify us now, but I am still totally convinced that we did the right thing. Hitler is the archenemy not only of Germany but of the world. When, in few hours' time, I go before God to account for what I have done and left undone, I know I will be able to justify what I did in the struggle against Hitler. God promised Abraham that He would not destroy Sodom if only ten righteous men could be found in the city, and so I hope for our sake God will not destroy Germany. No one among us can complain about dying, for whoever joined our ranks put on the shirt of Nessus. A man's moral worth is established only at the point where he is ready to give his life in defense of his convictions."