European Commission chief Jean-Claude Juncker paid tribute to Mr Kohl, describing him as the "very essence of Europe".
Kohl, who served from 1982 to 1998, made him the longest serving German chancellor since Bismarck.
In 2002, Kohl resigned from lower house of the parliament Bundestag and officially left politics.
"Throughout our endeavours, Helmut was a rock - both steady and strong". Kohl's trip with then-U.S. President Ronald Reagan to a war cemetery in Bitburg where SS troops were buried alongside ordinary German soldiers generated worldwide indignation. He also played an important role in advocating for the Euro, though the global currency was not introduced until after his term as chancellor. Within weeks, Kohl proposes an informal confederation that would lead to eventual German reunification.
"A great German has died", Gabriel said.
"We feel that a life has ended and he who lived it will go down in history", Chancellor Angela Merkel said Friday, her voice shaking with emotion.
"For Germans, he was a stroke of luck".
The head of the International Monetary Fund is expressing sadness at the death of former German Chancellor Helmut Kohl.
Georgian President Giorgi Margvelashvili also offered his condolences to the German people.
He says Kohl "will be remembered in Russian Federation as a staunch advocate of a friendly relationship between our countries".
Aware that Germany could be reunified only with the support of both the United States and the Soviet Union, Mr. Kohl developed close relationships with President George H.W. Bush and President Mikhail Gorbachev.
Still, Kohl couldn't stay out of politics entirely.
"He was deeply convinced that Europe was our destiny", Steinmeier said.
She added Kohl would always be remembered as the architect of Germany's reunification and for his European policy stance. The party leaders hinted that Kohl's tenure was more productive than his successors Gerhard Schröder and Merkel.
"They thought - and were right about it - that if Germany doesn't adopt the euro, nobody will".
He headed the government of Germany for 16 years, from 1982 to 1998. He became governor of the western state of Rhineland-Palatinate in 1969.
British Prime Minister Theresa May called the German politician "a giant of European history".
European leaders said the EU must build on his legacy. And Kohl was its chancellor. "A true European", Stoltenberg tweeted. The world has benefitted from his vision and efforts.
"Future historians will say Europe's 21st century began on his watch", former US President Bill Clinton said in 1999 when awarding Kohl the Presidential Medal of Freedom.
Clinton recalled a rally the leaders had attended together in the former East Berlin in 1994 and the "genuine hope in the eyes of tens of thousands of young people".
The late French President Francois Mitterrand and then German Chancellor Helmut Kohl stand hand in hand as they listen to the national anthems during a French-German reconciliation ceremony outside the Douaumont cemetery near Verdun, eastern France in 1984.
"This man who was great in every sense of the word - his achievement, his role as a statesman in Germany at its historical moment - it's going to take a while until we can truly assess what we have lost in his passing", Merkel said at a news conference, according to a translation by German publication Deutsche Welle.