The atrocities carried out under the rule of Nazi Germany showed our ability for almost unimaginable cruelty towards one another and, probably for the first time, they were carried out with scientific precision.
Plenty of people inside and outside of Germany and the other occupied countries knew, or at least suspected, what was going on, though few could or did do anything about it.
We're familiar with some of those who did. Oskar Schindler is perhaps the most famous due to Steven Spielberg's film, but there were many individuals and groups who risked their lives for other people, not just Jews (Wikipedia has a partial list of those who helped Jews, while the most prominent are featured in a list of the Righteous among the Nations).
It's perhaps not unsurprising that I'd never heard of the person celebrated in an email I received recently. Irena Sendler was part of the Polish Underground, who helped Jews throughout the war. She focused on helping children, though she also produced false documents for Jewish families before that, and managed to save at least 2,500 children by smuggling them out of the Warsaw Ghetto.
She managed this because she was allowed to enter the Ghetto to check sanitary conditions for typhus (according to Wikipedia, the email I received suggests she was a plumbing/sewer specialist).
The email stated that she smuggled the children out in the bottom of her toolbox and in a burlap sack in the back of her truck, training her dog to bark at the security checkpoint to cover any noise the children made.
She kept lists of the children and their original names so they could be reunited with their parents after the war, but many of them were killed in the concentration camps.
Despite being caught, tortured and scheduled for execution, Irena managed to escape by bribing some guards.
She is just one of many who risked their lives to help others in the face of persecution, one of many who stand as a reminder of the brightest of humanity even in the darkest of times.