The famous Iranian-born photographer Abbas, who covered wars and revolutions across the world during a glittering career behind the lens, died on Wednesday in Paris, his Magnum photo agency said.
Abbas, who was 74, joined Magnum in 1981 and covered conflicts and unrest in Bangladesh, Vietnam, the Middle East, Iran, Chile and Cuba as well as documenting South Africa under apartheid.
"He was a godfather for an entire generation of young photographers," Magnum president Thomas Dworzak said.
"An Iranian transplanted to Paris, he was a citizen of the world who documented without rest wars, disasters, revolutions and uprisings."
Abbas was "a great gentleman and one of the best photographers I have ever met," Jean-Francois Leroy, director of the 'Visa pour l'image' photography festival in Perpignan, southern France, wrote on Twitter.
"Abbas was a great among the greats," Reporters Without Borders president Pierre Haski said on Twitter. "His work was huge and covered so many areas."
Haski also tweeted this famous photo that Abbas took during his time documenting apartheid.
Abbas travelled the world to learn about religion, a fascination born out of the Islamic Revolution in his home country, which he covered from 1978 to 1980, before exiling himself for 17 years.
"He is someone who had big and very committed documentary projects, and for the long term," said photography historian Clara Bouveresse, author of a reference book on Magnum. "His book on the Iranian revolution in 1980 was a way of telling this event in detail with a sequence, a narration. He was someone for whom the way of organising images, of sequencing them, counted enormously," she said.
Abbas documented Islam around the world from 1987 to 1994, publishing Allah O Akbar: a journey in militant Islam, before focusing on Christianity, animism, Buddhism and Hinduism.
"For him, the work of the photographer did not stop at the moment when he pressed the shutter. It continued in the selection of images, the proofreading of the work and in the production of a story," added Bouveresse.