Raoul Wallenberg was a young diplomat posted in Nazi-controlled Budapest during the war and he saved the lives of thousands of Jews by providing them with Swedish documentation.
He has been compared to Oskar Schindler, the German who is credited with helping 1,200 Jews by employing them in his factories.
As the war drew to a close, Wallenberg disappeared, and his final moments remain a mystery.
Soviet officials have claimed Wallenberg, who went missing 70 years ago on Saturday, one day after the Soviet army invaded the Hungarian capital, died two years later in a Moscow prison but experts and diplomats have disputed that claim.
Now, new information links Wallenberg – only the second foreigner to become an honorary citizen of the United States, after British wartime Prime Minister Winston Churchill – to German businessman Ludolph Christensen.
In the early 1940s, Wallenberg was an executive in the Swedish trading company Mellaneuropeiska AB, which managed to import to Sweden large quantities of foodstuffs, including speciality items such as cigarettes and fruit, which were hard to obtain due to the war.
While these transactions have been well-known, it has now emerged that almost all of them were carried out in cooperation with Ludolph Christensen, according to an article published on the website raoul-wallenberg.eu.
Christensen was protected by General Karl Wolff, right-hand man of SS leader Heinrich Himmler, one of the main architects of the Holocaust, which Wallenberg was fighting.
The relationship "shows the complexity of trade relations in times of war and could provide new ways of solving Wallenberg's disappearance," the study's authors, Susanne Berger, Vadim Birstein and Craig McKay, wrote.
New evidence uncovered by the researchers also shows that the German businessman also met Wallenberg at the start of his Budapest mission, in the summer of 1944.
"This does not diminish his accomplishments in Budapest in any way, but the contacts may have deepened Soviet suspicions about his person and his work," Berger told AFP.
Ingrid Carlberg, author of a comprehensive biography of the Swedish hero, welcomed the new discovery but told AFP the "relationship may not have been decisive in the arrest of Wallenberg."
Raoul Wallenberg is President Obama's personal hero and he was posthumously presented with a Congressional Gold Medal in July 2014.
In 2013, the Swedish Academy made August 27th Raoul Wallenberg Day to commemorate his legacy each year.