WILLIE DONALDSON was a man of parts — among them Talbot Church, Liz Reed, Jean-Luc Legris and, most famously, Henry Root, the wet fish merchant and eccentric right-wing bigot who wrote to prominent public figures offering comment, advice and support — often in the form of a one pound note. Root’s outrageous yet deadpan missives succeeded in provoking a range of often embarrassingly positive responses from the likes of Esther Rantzen, Larry Lamb, Lord Grade, Sir David McNee (the then Commissioner of the Metropolitan Police), and Root’s personal and political heroine, Margaret Thatcher. The resulting book, The Henry Root Letters (1980), was a bestseller for months.

The Root letters spawned a number of sequels, one of which was made into the television programme Root Into Europe (1992) starring George Cole (of Minder fame). They made Donaldson rich, not for the first time in his life, and secured his place as a cult figure among 20th-century satirists.

His other works included further forays into celebrity ridicule, a number of autobiographical works and some impressively researched (if at times factually dubious) reference books: Rogues, Villains and Eccentrics — an A-Z of Roguish Britons Through the Ages (2002) and I’m leaving you Simon, you disgust me. . . — A Dictionary of Received Ideas (2003). None achieved the same degree of acclaim as the Root letters, but all displayed their author ’s cultivated cleverness and the captivating, if rather destructive, roguishness by which he lived.

Charles William Donaldson’s privileged background had set him up for a life of self-indugent and reprehensible behaviour. There was also, however, a subtle intellectual competitiveness which manifested itself in his witty and biting attacks on bourgeoise values. A man who empathised with Flaubert’s disgust at his brainless peers — his Dictionary of Received Ideas was intended in part as the realisation of a project Flaubert had not been able to complete — he claimed that he felt more at home with thieves and prostitutes than intellectuals.

But he could also be self-effacing and charming. He said that his own writing “is all about showing off, it’s not serious. It’s why my journalism was so rubbish”. He was at various times a columnist for The Independent, a diarist for the Mail on Sunday, restaurant critic and book reviewer.

His charisma was such, that even some of his lovers, who he treated abominably, continued to speak of him with affection. The singer Carly Simon described him, years after he had taken up with another woman while she was in the US preparing for their wedding, as a “wonderful, wonderful person: the funniest man I have ever met”. Not everyone held him in such high regard.

His sexual depravity and nefarious lifestyle were notorious. He had attended Winchester College, which instilled in him, he believed, his intellectual insecurity and his sexual immaturity. His recollections of his time there are published in From Winchester To This (1998) — for which, he said, the libel report was longer than the published book. Among other things, the institution had taught him that “sex is a dirty and embarrassing thing,” for which reason prostitutes suited him far more than conventional relationships. He lost his virginity to a Parisian whore when he was 18.

Before going up to Magdalene College, Cambridge, he did his National Service as an officer in submarines and spent a year teaching at a London crammer. His mother died in a car crash when he was in his teens, and his father, chairman of the Glasgow-based Donaldson Shipping Line and an alcoholic, died two years later. Donaldson, by then at university, was left an inheritance of almost £350,000.

His money went on literary ventures and theatrical productions; he spent little time studying for his English degree. After university he was the lucky impresario who, as co-producer, launched Beyond the Fringe, bringing together Jonathan Miller, Alan Bennett, Peter Cook and Dudley Moore in 1961. He was also the first serious promoter of Bob Dylan in the UK. Nevertheless, despite these successes, a series of theatrical flops soon brought bankruptcy. He did not suffer the ignominy of this setback for long, however, as another large inheritance in 1968 meant that he again found himself more than comfortably off.

By then he was already married to his second wife, with numerous colourful liaisons behind him. He first married Sonia Avory, a debutante who seems to have interested him little, in 1957, but he left her and his infant son for the then wife of the journalist Jeffrey Bernard; she stood him up the night he terminated his marriage, explaining three days later that they were “ships that passed in the night”. He had a love affair with a dancer in Summer Holiday, moved in with the actress Sarah Miles, then with Carly Simon and then, in 1968, married another actress, Claire Gordon.

It was at this time that he discovered cannabis. The parties he hosted became famous for their extravagance and excess and were populated by the eccentric and uninhibited. The steady flow of drugs and call-girls was expensive to keep up, however, and in 1971 Donaldson fled to Ibiza. There he spent his last £2,000 on a glass-bottomed boat. It brought him no luck, and he was forced to scavenge for food on the beach. He decided to return to England when he heard that a former girlfriend had opened up a brothel on the Fulham Road. She supported him for a while, and his time there was the basis of his first novel, Both the Ladies and the Gentlemen (1975).

Within a few years, the phenomenal success of the Root letters had put him back in funds. The Further Letters of Henry Root (1980), Henry Root’s World of Knowledge (1982), Henry Root’s A-Z of Women: “The Definitive Guide” (1985), The Soap Letters (1988), Root into Europe (1992), and Root about Britain (1994) further mined the same lucrative seam.

To the end, Donaldson’s personal life continued in shambolic vein, some of its more lurid aspects documented in his 1987 novel Is This Allowed? In the 1990s a girlfriend introduced him to crack cocaine, and he became addicted. It failed to kill him, but it reduced him to bankruptcy once more. Yet he was always both stylish and curiously efficient when it came to his work. Despite the parties, the drug-taking and the complicated love affairs, he rarely missed a deadline. Whatever the damage he inflicted on himself and others, he saw it as a saving grace that he could write. Donaldson is survived by his third wife, Cherry Hatrick, from whom he was separated, and by the son of his first marriage.