During the war, Tendera was sent to Auschwitz after being arrested by the German secret police, the Gestapo.
While in the camp, he was subjected to pseudo-medical experiments conducted by German doctors.
After the war, Tendera worked with the Centre for Dialogue and Prayer at the site of former Auschwitz death camp in Oświęcim, southern Poland, and he also worked with the Auschwitz-Birkenau Memorial Foundation based in the Polish city.
Tendera was known for his efforts to counter historically inaccurate references to Nazi German death camps in occupied Poland.
He sued German public television broadcaster ZDF for referring to the Auschwitz and Majdanek concentration camps in 2013 as “Polish.”
Both camps were run by the Nazi Germans in occupied Poland during World War II.
Polish President Andrzej Duda has noted Tendera’s passing in a Twitter post.
He said: “Mr. Karol Tendera has passed away. He was a prisoner of the German Auschwitz camp; his camp number was 100430. Until the last moments of his life, he steadfastly fought for historical truth and his struggle was victorious. A wartime prisoner, a hero of our time. RiP.”
In 2016, a district court in the southern Polish city of Kraków ruled that Germany’s ZDF had damaged Tendera's dignity and national identity by referring to the Majdanek and Auschwitz camps as “Polish.” The court ordered the broadcaster to apologise.
The use of historically inaccurate terms by some international media has sparked numerous complaints from Poland in recent years, prompting some news agencies to change their style guidelines and eliminate misnomers such as "Polish" death camps.
Public broadcaster Polish Radio last year launched a special educational website aimed at debunking misconceptions about Poland’s role in the Holocaust, at GermanDeathCamps.info.