Joseph Kennedy was one of the last of the American robber barons: born in 1888, he clearly absorbed the ethos – or lack thereof – of the gilded age, an era of corruption and covetousness, when tycoons such as Cornelius Vanderbilt and John D Rockefeller manipulated markets and monopolised industries. Kennedy's avarice seems so coldly all-consuming that it borders on the monstrous.

He recognised early that the young, decentralised film industry was ripe for "consolidation" – or monopolies. Using access to new archives and Kennedy's business files from his Holly­wood transactions, Cari Beauchamp's Joseph P Kennedy's Hollywood Years is a well-researched and revealing account of how he became, as Paramount Studio head Jesse Lasky's daughter later said, "one of the first and only outsiders to ever fleece Hollywood". But while Hollywood may sound like fair game, Kennedy fleeced – and destroyed – many individuals along the way. During his four years there, between 1926 and 1930, Beauchamp estimates, he made at least $9m – in an era, as she notes, when the average per capita income of Americans was $681. He left, as the great depression began, worth an estimated $15m (roughly equivalent to £500m today), having avoided the consequences of the crash he had helped to cause by artificially driving up prices, and then escaped by selling short, early and often. "Joe always wore a wide grin on his face," said Betty Lasky, "to camouflage the dollar sign imprinted on his heart." Double-dealing was his standard operating procedure, in both personal and financial exchanges. He charmed people into trusting him and then took them for all they were worth. The only exception to what seems a nearly sociopathic lack of empathy was his devotion to his children – but anyone so monumentally self-interested presumably considered them to be extensions of himself.

If Kennedy's duplicity was not limited to finance, neither was his rapacity. Beauchamp quotes Jack Kennedy opining that his father was driven by vanity. But a more accurate word seems "cupidity": even his lechery was prompted by compulsive acquisitiveness. Kennedy's notorious relationship with Gloria Swanson, which Beauchamp details, was representative. Extravagant and hopeless with money, Swanson was half a million dollars in debt when she met Kennedy, despite being one of the world's highest-paid movie stars. He set up a production company, advised her, got into bed with her, flaunted their relationship to acquire her glamour – and made sure her company paid his for everything. When they split up after three years, she was $1.5m in debt and he had profited to the tune of many millions more. Swanson later said Kennedy operated "like Stalin": "Their system was to write a letter to the files and then order the exact reverse on the phone." She wasn't wrong. Kennedy was a swindler on such a grand scale that people were forced to respect him, but a swindler is all he was. He always operated within the law (because financial regulations were so lax), but he rarely operated ethically. In a nice historical irony, after leaving Hollywood he was made head of Roosevelt's new Securities and Exchange Commission because, as FDR shrewdly observed, "It takes a thief to catch a thief."

Happily, this meticulous biography remains content to digest the discernible facts of Kennedy's Hollywood dealings while never attempting to explain away his greed: it simply drove him, as fatal a flaw as his hubris. His sons weren't the only casualties of Kennedy's ambition: he had his daughter Rosemary lobotomised. He may have meant well (it was considered cutting-edge treatment in 1941), but he seems to have felt that her mental problems might damage the family's reputation; moreover he informed neither his wife nor their eight other children. When the surgery left Rosemary with "the mind of a small child", he institutionalised her; she simply disappeared, and he informed the family that Rosemary was "teaching in the Midwest".

Beauchamp's focus on the bottom line, while it doubtless would have gratified Kennedy, does mean that she occasionally sacrifices historical context. When Kennedy comes into contact with Paul Bern, it is not mentioned that he would soon marry Jean Harlow and be found shot in the head shortly after. The scandal and probable cover-up was one of the milestones of the age, suggesting the intimacy and incestuousness of early Hollywood powerbrokers. But she argues persuasively that Kennedy set the pattern for Hollywood today: bankers controlling the studios, rather than film-makers.

In his monetary dealings, Joe Kennedy was a democrat: he would screw almost anyone. Otherwise, his politics were closer to fascism: his advice to the overwhelmingly Jewish heads of film studios during the second world war was to appease Hitler by ceasing to make "anti-Nazi pictures". What Kennedy learned best from Holly­wood, however, was the importance of branding and myth-making: he was an early manipulator of the cult of personality. His talent for pious façades camouflaging covert manipulation only came to fruition with his sons' political careers, as he instructed them: "It's not what you are, but what people think you are that is important." Fortunately, scrupulous biographies such as this help ensure that what we think of Joe Kennedy is precisely what he so richly deserved.