And the White House and official records indicated Thursday that -- as with many a family legend -- the facts may indeed be a bit different.
Biden paid tribute to his uncle, 2nd Lieutenant Ambrose J. Finnegan, after visiting a war memorial during a campaign trip to the president's hometown of Scranton, Pennsylvania on Wednesday.
The 81-year-old president, who was aged one when his uncle died in 1944, reached out to touch Finnegan's name which was engraved on the monument.
"He got shot down in New Guinea, and they never found the body because there used to be a lot of cannibals, for real, in that part of New Guinea," Biden later told an audience of steel workers in Pittsburgh.
Biden also repeated the story to reporters, adding that "he got shot down in an area where there were a lot of cannibals in New Guinea" and that the US government had recovered parts of the downed plane.
The problem?
His account of his uncle's death, and his possible cannibalization, differs from US defense records.
The official Defense POW/MIA Accounting agency said that Ambrose Finnegan's plane was headed to New Guinea on a courier flight and was "forced to ditch in the ocean" off the island's coast "for unknown reasons."
The aircraft hit the water hard and three crew members failed to emerge from the sinking wreck, while one survived and was rescued by a passing barge, it said on its website.
"An aerial search the next day found no trace of the missing aircraft or the lost crew members," it said.
White House Press Secretary Karine Jean-Pierre confirmed that Ambrose Finnegan "lost his life when the military aircraft he was on crashed in the Pacific after taking off near New Guinea", not over land.
But she defended Biden, saying it had been "incredibly emotional and important" to the president to be able to honor his uncle at the memorial.
Biden "highlighted his uncle's story" to show support for veterans and draw a contrast with election rival Donald Trump, who reportedly disparaged military members killed in war as "losers" and "suckers" while president, she said.
The issue is personal to Biden, whose elder son Beau was a veteran of the Iraq war and whose death from brain cancer the president attributes to military "burn pits" used to incinerate waste.
Historically, cannibalism has been reported Papua New Guinea, the Pacific nation that occupies the eastern half of the island of New Guinea, off the northern coast of Australia.
