I have read several biographies of Rudolf Steiner (1861-1925) - including his partial Autobiography, which I would recommend (albeit it is not factually reliable, but more of an apologia working from the covert agenda of explaining 'why I was always right').
However, none of the biographies greatly impressed me so far except for volume two of Peter Selg's seven (!) volume study; which is that covering the years 1890-1900.
This was the period after Steiner finished University and began seven years of editorial work on a collected edition of Goethe's scientific writings, in Weimar; then moved to become a journalist in Berlin.
This is also the period when Steiner wrote his PhD thesis (now published as Truth and Knowledge) and his major philosophical work The Philosophy of Freedom.
It was also the period when he began his remarkable career as a lecturer, and (around 1898) became a Christian. This was a major and sudden change, since up to the early 1890s, Steiner was apparently anti-Christian (according to his writings), moving in radical anarchist circles; also deeply engaged with the work of Nietzsche (befriending for a while Nietzsche's sister, and meeting the mute and demented philosopher; and having published a book about him in 1895).
I am currently reading the first volume of Selg's biography (1861-90) having read all but one of the later volumes). So far there is very little detail beyond what was reported by Steiner retrospectively and many years later.
Indeed, his early years are extraordinarily poorly documented, for such a famous and influential man. It seems that none of his thousands of disciples made any serious attempt to collect information while he was alive or just after. Or perhaps enough effort has not yet been made?
But I am looking forward to the later years, from when Steiner studied at the Vienna Institute of Technology; where I anticipate more in the way of external corroboration from independent sources.
In general, nobody has so far been much interested in Steiner except for his followers (Colin Wilson and Gary Lachman's overviews probably make the best starting point); and Anthroposophists seem incurious to seek beyond what Steiner himself said about himself. This is not difficult to understand, given the past and continuing attitude to Steiner within the Anthroposophical Society...
In Steiner circles, he is not really seen as a Man - but as something more like an angel or deity whose entire vast work is necessarily necessary, coherent and of timeless relevance. It would be blasphemous for any normal person to select-from, critique, let alone criticize, such an individual.
For example, Stanley Messenger was asked in the Q&A after a talk whether Steiner had ever made an error; and SM was unable or unwilling to mention even one instance - but instead said that Steiner may sometimes have been misunderstood.
Even Owen Barfield - a major genius in his own right, as well as (probably) Steiner's greatest follower and developer - never (to my knowledge, in print) allowed himself to reject anything ever written by Steiner; the furthest OB would go was to state that he did not speak about that which he had not, yet, confirmed.
So, I am not exaggerating. And this attitude serves to maintain the near-total neglect of Steiner, who was certainly a major genius and of vital relevance to these times; but who (to one outside the charmed circle) was a also flawed character, most of whose work outside of philosophy and the history of consciousness can and should be ignored or set-aside.
Nonetheless, as a major genius with such vital things to say; I find myself driven to continue exploring Steiner's biography, through the available channels; and to draw my own conclusions.