Cecil John Rhodes is now the imperial archvillain, a symbol of all that “must fall” in a decolonised South Africa. His statue at the University of Cape Town was doused in pink paint and then, as demanded by the student protesters, removed to a vault somewhere. Yet his legacy, insofar as it includes a united South Africa and the mining base of our economy, is still with us.

And the man remains something of an enigma: a megalomaniac who believed God’s support for his cause was evident in every stroke of luck, but also a sensitive soul who grieved wildly and publicly for his dead secretary, Neville Pickering.

Rhodes spent much of his time in South Africa living in shacks near his mines, even as he was amassing the huge fortune that would underpin his colonial projects while he lived and ensure that they were pursued after his death.

Villain or not, he was a complicated man, something of a chameleon with vastly different aspects contained within him – even a bit of a multiple personality.

“I count at least five characters in him,” says Robin Brown, author of the new book The Secret Society: Cecil John Rhodes’s Plan for a New World Order (Penguin). Acknowledging that, for at least the first half of the 20th century, most books about Rhodes treated him heroically, before the tide turned and the anti-colonial view condemned him as a ruthless robber baron, Brown says: “We need an honest account of Rhodes.”

In The Secret Society, Brown explores the enigma of Rhodes, delving into his homosexuality more deeply than any work on him so far and showing how Rhodes’s dreams of an expanded British empire were codified early in his career and were then played out, through the efforts of members of his inner circle, at least until the end of World War II, when Britain began to let go of its imperial possessions.

One of the puzzles in Rhodes’s life story is his time at Oxford University. Having made a lot of money in Kimberley, becoming a millionaire by age 20, Rhodes then signed on for a degree at Oxford. But his time there was oddly muted – he may have gone drinking with fellow members of the Bullingdon Club, and he may have been devoted to classics such as the Meditations of Marcus Aurelius, but he doesn’t seem to have done much at Oxford: he took many years to get his degree, and it wasn’t a particularly good one anyway. This indifferent attitude seems strange in a man so obviously driven to accumulate wealth and power.

What was really happening, says Brown, was that Rhodes was working on the formation of his secret society, which would pursue the aim of an almost universal Pax Britannica. At Oxford, Rhodes wrote his Confession of Faith, which was appended to his first will: it set out his belief in British supremacy as well as his plans to create a dedicated group to serve the cause of empire.

As soon as he got back to Kimberley, Rhodes set up this group (called only “the Secret Society”), the core of what would become a set of very influential politicians and, as it evolved into more public forms, would develop into a series of important institutions that today include the foreign policy think-tank Chatham House, the Mandela-Rhodes scholarships, and much more.

In this respect, Brown’s book is as much a biography of Lord Alfred Milner as it is of Rhodes. It was Milner, ultimate heir to Rhodes’s fortune, who picked up the baton when Rhodes died. A man of almost monklike austerity, Milner was something of a contrast to the flamboyant Rhodes, but it was he who made sure Rhodes’s plans for the future (mostly a “new world order” that looked very much like a global British empire) were carried forward.

The secret society expanded and went more-or-less public, creating the empire-supporting Round Table as an open platform for its aims. Yet an extraordinary number of highly influential politicians and lobbyists were either members of the original secret group or fellow travellers.

Brown details how these influences played out on the eve of World War II, when the Nazi-linked king of England, Edward VIII, abdicated, believing perhaps that he would soon be back as a Nazi monarch. There is even more on this murky business, says Brown, that has emerged since he finished The Secret Society. He will soon be working on a follow-up.

Weaving his own story into the book, Brown tells how his family was among the 20th-century “pioneers” who travelled to Rhodesia (now Zimbabwe) to help populate it with ­English-speaking white people – a key aspect of Rhodes’s dream.

Brown, who has worked in television, making nature documentaries, for most of his professional life, has also written books about Great ­Zimbabwe and his family story in Southern Africa. Now, with The Secret ­Society, he says, that makes three books at least part-inspired by Rhodes and his legacy.

“This story has chased me,” he says, “and it keeps going.”