Try to imagine you are Dan Rather. All you’ve ever wanted is to tell a story. You begin working as radio and television reporter in Texas in the 1950s. You work hard, you’re confident. In 1961 you are hired by CBS News. It is the big time, a heady environment, a network with character, moulded by the revered broadcaster Edward R Murrow, your hero. You are surrounded by scholarly correspondents who have style and experience. You want the approval of your peers and they have high standards. You up your game, you are loyal, hard-working and ambitious. You want to be one of them.

You report on big events. The assassination of John F Kennedy, Vietnam, Watergate and Richard Nixon’s resignation. You build your reputation and gain authority. CBS News is your home. After 20 years growing a following, in 1981 you take over as anchor of the evening news from another legend, Walter Cronkite.

From this moment on, you are as recognisable as the president of the United States – and the global communications revolution will beam your face to millions of homes by satellite and cable around the world. You achieve power, influence and notoriety, not to mention the multi-million-dollar salary. At 6.30pm, five nights a week, you become not just the face of American news but the face of America. You command huge budgets. You may be in the studio, or you might decide to take the whole news crew off to the wedding of Diana and Charles, a papal funeral, or Baghdad. You will present the news of the world to millions of Americans – and, with an avuncular and affectionate, even folksy sign-off, you will send them to bed reassured that no matter how bad it is out there, they’ll be safe until tomorrow. You are not just the network’s anchor: some regard you as the nation’s anchor, a calming trustworthy voice in a world of fear, hate and dispute.

You are infallible, unimpeachable – and then, in 2004, a scoop lands on your desk. With your famous knitted brow and resonant concern, you tell America what you know. But this story explodes in your face: it shreds a reputation built over 50 years and eviscerates your world. Your career, as one of the biggest influences on what America has thought for half a century, is dead. Was it suicide? Or was it murder?

“People will scoff. But I always thought I tried to reach a person or a couple,” says Dan Rather, explaining how he built up an audience in 13m American homes. Such was his influence that if he wore a pullover on a story, it would become news itself, to be deconstructed: “Is Dan Rather trying to project a warmer image?” Viewer approval meant ratings, meant advertising revenue, meant millions. In 1987 he walked off set when a prolonged tennis match threatened to delay the evening news, and for six minutes CBS broadcast “dead air” while producers searched for him. He appeared on The Simpsons, and his unshaven face reporting from Afghanistan kicked off the recent hit movie Charlie Wilson’s War. He wept on the Letterman show in the wake of 9/11, and REM dedicated a rock anthem to him in 1994. Rightwingers branded him “liberal” and democrats regarded him as a crusader.

Dan Rather became a part of American folklore. He was the longest-serving anchor if American news – there for nearly 25 years. But at CBS he was also the managing editor, the man who was personally responsible. It was a role he sought – and when the story blew up in his face, who else was there to blame?

In September 2004, Rather delivered a piece for the 60 Minutes programme on President Bush’s service record with the Texas Air National Guard. There were memos written by Bush’s former commanding officer, the late Jerry B Killian, that said Bush’s military record had been sugar-coated and he’d received special treatment.

The aftermath centred on the authenticity of the documents. They were attacked by right-wing fanatics for being forgeries and the mainstream media picked up the story. Rather defended his report, but when authenticity could not be proven, he made an apology on the air, saying: “… if I knew then what I know now, I would not have gone ahead with the story.”

What happened next is complicated. The simplified version is that CBS commissioned an independent investigation, led by the former US attorney-general Dick Thornburgh, a Bush family friend. It became obvious to Rather that his employers were not backing him up. He was told to cease efforts to prove the documents were authentic and was interrogated before the commission. Rather believes that Sumner Redstone – chairman of Viacom, which was then CBS’s parent company – wanted him out. And that this was an orchestrated campaign.

Was it political pressure from the Bush administration that CBS bowed to, an opportunity to boost ratings by dropping the stubborn ageing anchor for a younger, fresher face? Or was Rather hoisted with his own petard, the man responsible for the scoop that couldn’t be proved, who had to fall on his sword?

In January 2005, the producer of the story and two other people were fired. Rather retired as anchor in March of that year. After that, he was rarely seen on the air, and in June 2006 it was announced that he would be leaving the network. It was not an amicable parting.

Then, in September 2007, Rather came roaring back into the public eye. He filed a $70m lawsuit against CBS, Viacom and Sumner Redstone; the CBS chairman, Leslie Moonves; and the former CBS News president Andrew Heyward. He is suing them for breach of contract and breach of fiduciary duties – for making him the fall guy in the Killian story and destroying his reputation. It’s a giant legal battle that some believe takes courage to fight, but others believe is the foolish and hubristic act of a man with damaged pride.

Times Recommends

• Over the Wall
• Why Africa welcomes the ‘new colonialism’
• Which will come out on top: paper or gold?