I'm fan of Roger Penrose

One of the greatest physicists, and still active in research in his 80s, is Roger Penrose.  Penrose has been working mostly behind the scenes for a long time, never having got the exposure of his friend and collaborator Stephen Hawking, and yet Penrose is at least Hawking's equal.  

When the theory behind black holes were being examined in the 60s and 70s, there were still many questions about what happened inside them (there still are), and one of those questions was whether or not anything that fell into a black hole could ever miss being crushed to destruction at the centre of the hole.  Penrose showed that no object could ever miss the centre of a simple black hole, and he did it using not physics but topological mathematics, a stunning achievement.  Penrose is one of those who revolutionised our understanding of these strange collapsed stars.

Penrose seems to like sometimes standing on the sidelines of physics, challenging established ideas and coming up with amazing new ways of looking at reality.  One of his challenges to such ideas is his rejection of the idea of inflation, the idea that the universe expanded incredibly fast right at its origin.  This expansion is supposed to have smoothed out the universe, creating a state of very low entropy, from which the universe we see around us could have formed.  Penrose says that inflation solves little, as inflation itself requires such special conditions that it's more unlikely than the smoothness it's supposed to explain.  Instead, Penrose has come up with some fascinating ideas of what the universe may have started like and what it may end up like, as discussed in his latest book "Cycles of Time".  As the physicist Lee Smolin says, only Penrose could write phrases like "after eternity" and really mean it!

Penrose does have some strange ideas, such as that minds can do things that computers can't, or that consciousness may be a quantum phenomenon.  However, he does have the honesty to admit in his writings that his views aren't mainstream.  I find that honesty both endearing and important.

His books can be dense with information, and hard to get through, but if you can, it's really worth it.  You will always learn something new, and get an exciting perspective on physics from one of the greats.