Peter Woit in Not Even Wrong:
While away on vacation, I heard last week the sad news of the death last week of Michael Atiyah, at the age of 89. Atiyah was both a truly great mathematician and a wonderful human being. In his mathematical work he simultaneously covered a wide range of different fields, often making deep connections between them and providing continual new evidence of the unity of mathematics. This unifying vision also encompassed physics, and the entire field of topological quantum field theory was one result.
I had the great luck to be at MSRI during the 1988-89 academic year, when Atiyah spent that January there. Getting a chance to talk to him then was a remarkable experience. He had one of the quickest minds I’ve ever seen, often grasping what you were trying to explain before the words were out of your mouth. At one point that month I ran into Raoul Bott walking away from an ongoing discussion with Atiyah and Witten at a blackboard. Bott shook his head, saying something like “it’s just too scary listening to the two of them”.