Mr Kohl, who has used a wheelchair since fracturing his hip last year, added: "There has never been a relationship that reached the level of my relations with these two gentlemen."
Correspondents say the trio clearly enjoyed each other's company at their first reunion in many years.
Mr Bush, 85, who was US president from 1989-93, said the historic events behind the wall's collapse had grown "in the hearts and minds of the people who so long had to strive for their God-given rights".
"The wall could never erase your dream, our dream of one Germany, a free Germany, a proud Germany," he said.
Newly re-elected German Chancellor Angela Merkel was among the dignitaries who attended Saturday's reunion.
"The people were the heroes," said Mr Gorbachev, 78. "The three of us don't want to take credit for the accomplishments of the previous generations."
The last Soviet leader also remembered two absent Cold War leaders: former British Prime Minister Margaret Thatcher, who has dementia, and ex-French President Francois Mitterand, who died in 1996.
Mr Bush, now walking with the help of a cane, was full of praise for Mr Gorbachev, a Nobel Peace laureate who was in office between 1985-1991.
"Through it all he stood firm, which is why he'll also stand tall when the history of our time in office is finally written," said the former US president.
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