One of the iconic physicists of our time has passed. I'm certain that many of us own the book "Gravitation".

For a 2nd time this year sad & amazing news for the spaceflight - astronomy - cosmology world

Very sad news. I still vividly remember reading, as a teenager many years ago, about his idea that there is only one electron in the universe, which travels from the beginning of time to the end of time, and back to the beginning, over and over. Among his greatest accomplishments:

Introduced the S-matrix
Pioneer in the theory of nuclear fission
Introduced the words 'wormhole' and 'black hole' into physics/cosmology
Pioneer in the theory of quantum gravity

A short biography can be found at wikipedia