The heroism is indisputable. In spite of the long years of suffering in the grip of motor neuron disease, Hawking has survived at the pinnacle of the difficult and competitive discipline of speculative physics. As yet, his main insights remain contentious, but, right or wrong, he is among the half-dozen or so grandmasters of his art.
The magic is another matter. It began five years ago with the publication of A Brief History of Time, his popularisation of the leading ideas of contemporary physics. Before that book, he was well known to a few, dimly known to a few more and completely unknown to most. But, for mysterious reasons, that book sold millions around the world and turned him into science's one global superstar.
Hawking the magus of physics is now a product of hype rather than reality. The claims made for his work are out of control.
He is not the equal of Einstein or Newton; he is simply one of the leading figures of modern physics, who happens to have found a successful way of popularising his subject. Yet the logic of publicity demands that he be elevated to the realm of ultimate, incontestable genius, there to become a kind of living monument for the intellectual tourist.
This may be seen as a trivial matter: hype creates many false images, many over-inflated reputations; real work carries on elsewhere regardless. But the problem is that neither A Brief History nor Black Holes and Baby Universes, Hawking's new book of essays, is a simply conscientious, informative popularisation of physics. They are tracts, they are propaganda. They are also arrogant and, whenever they stray out of the realm of physics, intellectually feeble.
I know that many will say I should not write in this way about a man condemned to such an extraordinary struggle in everything he does. I accept that Hawking the populariser may be a heavily edited product, quite distinct from Hawking the man.
But the books remain influential facts in the world. They advance specific arguments and abuse the efforts of others. They are open to dispute, however much the man's life may deserve respect.
The basis of the arrogance is Hawking's contempt for certain unscientific forms of knowledge. In A Brief History, this manifested itself as a brusque dismissal of modern philosophy on the basis of a quotation from Wittgenstein that Hawking had profoundly misunderstood. In the new book, this passing swipe becomes a more sustained assault. He complains about how philosophers have tried to categorise his way of thinking, and criticises them for being unable to keep up with 'modern developments in contemporary physics'.
As for the philosophers of science, 'many of them are failed physicists who found it hard to invent new theories and so took to writing about the philosophy of physics instead'.
This is horrific. The philosophy of science does not depend on keeping up with developments in one particular speciality; if it did, it would not be philosophy; it would be commentary. Philosophers of science, who include Descartes, Hume, Kant, Popper, Kuhn and Wittgenstein, have been engaged upon the most important and intractable task of our age: the formation of a fully human response to the superhuman success of science. To dismiss their efforts is to dismiss a central part of our culture and ourselves, Hawking included.
Nevertheless he feels justified in his abuse because, it seems, philosophers have accused him of being 'nave and simple-minded'. What he fails to grasp is that, philosophically speaking, the charge is fair, and he must expect this to be pointed out.
There are in this new book dozens of examples of confused, contradictory and imperfectly grasped philosophy, which I have not the space to list and disentangle. It need only be said that a certain abrupt, careless impatience combines with an alarming belief in his own publicity to produce some appalling nonsense.
At the heart of this nonsense is Hawking's fundamentalism. He tells us in this book that he rejected biology because it was 'not sufficiently fundamental', and that, from his boyhood, he wanted to do physics 'because it was the most fundamental science'.
This is a statement of faith and of scientific power-play more than it is a meaningful statement about physics. At other times, other sciences have been regarded as equally 'fundamental'. What Hawking is evidently drawn to is the feeling of being at the top of the scientific hierarchy, and of asking the most radical, most extreme questions about the nature of the world.
This leads him into competition not just with other sciences but also with entirely alien disciplines such as philosophy or theology. In the celebrated ending of A Brief History, he wrote: 'Then we shall know the mind of God.'
He was rightly criticised by myself and others for thinking that a highly specialised incident in the history of physics could justify any such claim, or that the role of 'God' in human culture could in any way be 'known' through a set of equations.
But in the new book he goes, if anything, further: 'We may not be forever doomed to grope in the dark. We may break through to the complete theory of the universe. In that case, we would indeed be Masters of the Universe.'
And from the thoughtfully included transcript of his appearance on Desert Island Discs: 'Love, faith and morality belong to a different category to physics. You cannot deduce how one should behave from the laws of physics. But one could hope that the logical thought that physics and mathematics involves would guide one also in one's morals.' This last is classic Hawking: the anodyne, populist statement for Sue Lawley and the listeners, followed by the fundamentalist hint that he may really think something quite different.
All this kind of material sits uncomfortably with further attempts to explain the outer reaches of physics in lay terms. What is significant about this awkward juxtaposition is that the physics and the philosophy never connect, except in the way the latter is given apparent authority by the former.
The admittedly thrilling and extraordinary nature of speculative physics works to convince readers that they are in the hands of a great and universal adept, and that this wizard will surely be as able to navigate the human realm as deftly as he does that of the stars.
The first danger of this kind of belief is that it diminishes and discredits science itself. Hawking's idea of science is that of a rarefied discipline far above the heads of ordinary people, and infinitely superior to all competing forms of knowledge. This is what justifies his own adopted role of scientist as universal sage.
At times people will be impressed by this, but at other times - in the wake, for example, of some scientific disaster - they will be disgusted; and ordinary, unpretentious scientists will have to apologise for these misleading and grandiose claims to authority and competence. Science can only ever work, and indeed exist at all, within a culture; it is a human artefact that will wither and die when it aspires to be something else.
The second danger is the corruption of language. Hawking's cavalier way with philosophy shows contempt for less robust forms of understanding.
He is impatient with claims he cannot test mathematically, because he fails to see that they are not there to be tested but to incorporate forms of wisdom more subtle, human and durable than anything in physics.
If his scorn is effective - and the sales of his book are an alarming indicator - delicate traditions of understanding and discourse will be threatened by his harsh rhetoric.
Hawking remains in his life a figure of great courage and heroism. Sadly, his books are arrogant and narrow-minded. The truth of this contradiction may be that the demands of marketing have created a false picture; that the great cosmic speculator has nothing to do with the impatient, patronising hack philosopher. That, anyway, is what I hope.
'Black Holes and Baby Universes and other essays' by Stephen Hawking is published on 21 October by Bantam Press at pounds 16.99.Reuse content