2 May 2016 Last updated at 18:12 BST
The announcement by Craig Wright that he was behind the Bitcoin virtual currency has sparked controversy.
Mr Andresen said evidence he had seen convinced him that Mr Wright is who he claims to be.
"He fits the kind of person I was interacting with way back in 2010," he told the BBC. "He provided cryptographic proof using the very first Bitcoin block to show he possessed that key."
The early Bitcoin blocks are the ones widely accepted to be connected to Satoshi Nakamoto - the pseudonym adopted by the creator of Bitcoin.
"To me he's proved it beyond a reasonable doubt."
Gavin Andresen, chief scientist at the Bitcoin Foundation, has spoken about the revelation that an Australian businessman was the founder of Bitcoin.