Wolff was the last commander of the Lincoln Battalion, a unit of American volunteers who fought for the Republicans in the Spanish Civil War. He took the position after the previous commander, Robert Hale Merriman, was killed.
The only US war he participated in was World War II, where he fought the Nazis on the Western Front.
Despite being in his 50s at the time, during the Vietnam War, he offered the service of himself and the other Lincoln Battalion veterans to Ho Chi Minh (Uncle Ho declined). After that, he became an anti-Apartheid activist as well as raising money for the Sandinistas.
Another good one is John C. Woods, American WW2 veteran. He was the hangman for many of the nazis convicted at the Nuremberg trials. It'll likely never be known for certain whether he botched those hangings deliberately or accidentally. But what is a fact is that most of the nazis he hanged did not die quickly from a neck-snap as hangings are supposed to go, but instead they died slowly and painfully of strangulation.