Code name: Fancypants

The eccentric story of the FBI provides fertile ground for a documentary series

Radio 4's history of the most famous acronym in the world must never end. At the time of writing, we are two-thirds through this ten-part series of 15-minute documentaries and deep into the bureau's struggle with the Hell's Angels - brought down in the 1980s by an undercover agent called Vernon, who was subsequently relocated and rewarded by having his tattoos drilled off. Stories like this make up for the fizz going out of things a little when J Edgar Hoover copped it back in episode six.

The FBI at 100 (broadcast daily, ends 14 March) presents the bureau as a kind of genius casting agent - adjusting its enormous fedora before selecting from a new crop of applicants precisely the right guy to wrap a body in rubber cement and pose as a draft-dodging millionaire at a South American casino. The series shivers with interviews with several of these snoops, articulate to a man, recalling how they were issued with hankies to keep their hands dry ("Hoover did not like a sweaty palm"), or the non-pleasures of sitting for days watching local dentists the boss was convinced were pinkos.

One of these guys had the same uplift in his voice as James Stewart - as if any inherent goodness within him were raising it up in sweet surprise at the world. He also had the code name Fancypants and he'd faced down the Mafia in an operation called the Pizza Connection. Fancypants was definitely the kind of guy you want in your tent pissing out. He once had a man under surveillance who proceeded to have sex on a desk with a woman who was not his wife. Fancypants called him up mid-act and said: "This is God. And ain't you ashamed?"

Mostly the agents kept defaulting to the subject of J Edgar, like smokers scanning the room for an ashtray. That Hoover was weird is no secret. He had very little chat. A solid veneer with concrete behind it. But the sweep of his moods was super-mysterioso. People with small heads made him gag, as did those who made left-hand turns in cars, and he once sent Martin Luther King an anonymous note that said: "You are no clergyman and you know it. You are an evil abnormal beast."

Not that Hoover had any time for the Ku Klux Klan, either. He would sit, pudgy in his Washington office, fingering his secret files, despatching his Nazgû to Mississippi, ordering them to "play with no rules" - by which he meant they were allowed to wear cowboy boots and chuck snakes into moving vehicles. They in turn recruited from within the Klan more than 20,000 informants, counter-agents and counter-counter-agents, so that by 1966 nobody could quite remember who was who or on which days they were required to be racist.

The crowning achievement of the series has been to allow its presenter, Tom Mangold, to speak in whole paragraphs. Man, he digs his subject. Like a director in a chair waving a megaphone, Mangold wields total control with his electric delivery, stopping off for a bit of contemplation, throwing up images of things to come. Wiretapping and Russkies, warrants and women, all the paranoid forces straining against the well-worn leash. And Vernon and Fancypants doing a right turn in a dark car, and then continuing on their way.

Pick of the week

1968: Myth or Reality?
Until end August, Radio 4
A season of programmes that explores the famous year of social and political upheaval.

Afternoon Play: The City Speaks
19 March, 2.15pm, Radio 4
First in a six-part series in which each episode is accompanied by a downloadable film.