The "Bookkeeper of Auschwitz" has died aged 96 before beginning a prison sentence for his involvement in the killing hundreds of thousands of Jews.
Oskar Groening was convicted in 2015 of being an accessory to the murder of 300,000 Jews at the Nazi concentration camp in occupied Poland during the Second World War.
Groening's role at Auschwitz rose to prominence when he gave interviews in 2005 about his work at the camp.
Groening (pictured left in the German army and right at trial in 2015) was in hospital when he died and had yet to begin his sentence.
He said he witnessed individual atrocities, but did not acknowledge participating in any crimes.
"The essential, nearly frightening, point about Oskar Groening is that he is one of the least exceptional human beings you are ever likely to meet", said author Laurence Rees, who interviewed Groening in 2005.
All of his appeals were rejected, and it was only his ill health that kept him from being sent to prison in recent years.
Efraim Zuroff, the head Nazi hunter for the Simon Wiesenthal Center, said it was unfortunate that Groening's conviction didn't result in "at least symbolic justice" for the victims of Auschwitz.
He was also on several occasions assigned to "ramp duty", processing deportees as they arrived by rail in cattle cars at the Nazi German death camp in occupied Poland.
Reinhold Hanning, a former Auschwitz concentration camp guard sentenced in 2016 to five years in prison as an accessory to the murder of more than 170,000 people, died last year without serving a day behind bars.
The legal basis for prosecuting former Nazis changed in 2011 with Germany's landmark conviction of former death camp guard John Demjanjuk.