Mr Yamaguchi had the bad luck to be in Hiroshima and then Nagasaki
The only person officially recognised as having survived both atomic bombings in Japan at the end of World War II has died from stomach cancer, aged 93.
Tsutomu Yamaguchi was in Hiroshima on a business trip on 6 August 1945 when a US plane dropped the first atomic bomb.
He suffered serious burns and spent a night there before returning to his home city of Nagasaki just before it was bombed on 9 August.
He said he hoped his experience held a lesson of peace for future generations.
It was already recorded that Mr Yamaguchi had survived the Nagasaki bomb, but in March last year officials recognised he had been in Hiroshima as well.
A handful or Japanese people are known to have lived through both attacks, but Mr Yamaguchi is the only one formally recognised by the Japanese government to have done so.
More than 200,000 people were killed in the two atomic bombings
Certification as a hibakusha or radiation survivor qualifies Japanese citizens for government compensation, including medical check-ups, and funeral costs.
On learning of his official recognition last year, Mr Yamaguchi said: "My double radiation exposure is now an official government record.
"It can tell the younger generation the horrifying history of the atomic bombings even after I die."
In his later years, Mr Yamaguchi gave talks about his experiences as an atomic bomb survivor and emphasised his hope nuclear weapons would be abolished.
About 140,000 people were killed in Hiroshima and 70,000 in Nagasaki.
Survivors fell sick with radiation-related illnesses, including cancers, for years after the bombings.
The Mainichi newspaper reported that last month Mr Yamaguchi was visited in hospital by James Cameron, the director of Titanic and Avatar, who is apparently considering making a film about the bombings.
Commenting on Mr Yamaguchi's death, the mayor of Nagasaki said on the city's website that "a precious storyteller has been lost".