Edward Snowden: The Greatest Whistleblower Ever?

As the fallout from the Prism leaks takes hold, we look at five of the most famous whistleblowers of all time.

Edward Snowden walked out of the murky shadows of the spying underworld and into the full glare of the media spotlight on Sunday when he revealed himself as the whistleblower behind the leaked documents relating to the National Security Agency's Prism programme.

The scale of the programme is huge, involving some of the best known companies in the world including Apple, Google, Facebook and Microsoft, and of course the US government which stands accused of monitoring the online activities of millions of people around the world.

It is for this reason that Daniel Ellsberg says "there has not been in American history a more important leak than Edward Snowden's release of NSA material."

And Ellsberg should know, he is the man behind the leak of the so-called Pentagon Papers over 40 years ago.

It means that Snowden joins a growing list of whistleblowers who for one reason or another used their position and data had access to, in order to reveal to the world previously unknown information.

Here we look at five of the most famous whistleblowers in history:

• Mark Felt (aka Deep Throat)

Until 2005 Felt was simply known to the world as Deep Throat, the whistleblower behind the Watergate scandal, but in 2005 following 30 years of denials, Felt revealed that he was in fact the person behind the leaks.

Having worked his way up to Associate Director, the second-ranking post in the FBI, Felt was working in an organisation which was battling for independence against the administration of President Richard Nixon.

It was the combination of his position, his reputation as a gossip and a motive which led Felt to leak details of Nixon's internal spies, secret surveillance, dirty tricks and cover-ups to the Washington Post reported that led to Nixon's unprecedented resignation on Aug. 9, 1974.

While Felt was not prosecuted for those leaks in 1980 he was convicted of a felony for violating the civil rights of people thought to be associated with members of the Weather Underground Organization, by ordering FBI agents to search their homes as part of an attempt to prevent bombings. He was ordered to pay a $7,000 fine, but was pardoned by President Ronald Reagan during his appeal

• JulianAssange

Assange is a highly polarising figure. Currently ensconced in the Ecuadorian embassy in London he is facing charges of sexual assault in Sweden but is best known for his work with WikiLeaks.

In 2010 Assange and WikiLeaks hit the headlines when it published US military and diplomatic cables through media partnerships with the likes of the Guardian. Assange, a hacker in his native Australia in his teenage years, was supplied the secret documents by Bradley Manning, a soldier in the United States army.

Manning is currently in court facing the possibility of life in a military prison for "aiding the enemy" and prosecutors say they have evidence which shows Manning and Assange collaborated to steal the top secret documents.

Assange has announced his intention to launch a political party in Australia and run a campaign for a Senate seat representing either New South Wales or Victoria in the Australian federal election.

• Daniel Ellsberg

As mentioned in the introduction, Ellsberg was the man behind the Pentagon Papers leak back in the 1970s. A US military analyst he was employed by the RAND corporation in the early 1970s and having been disaffected with the Vietnam War for some years decided to do something about it.

In late 1969, along with former RAND Corporation colleague Anthony Russo and the staff of Senator Edward Kennedy, Ellsberg decided to leak a top-secret Pentagon study of US government decision-making in relation to the Vietnam War, to The New York Times and other newspapers.

They revealed that the government had knowledge, early on, that the war could most likely not be won, and that continuing the war would lead to many times more casualties than was ever admitted publicly and that the Johnson administration had "systematically lied, not only to the public but also to Congress, about a subject of transcendent national interest and significance."

Ellsberg and Russo were charged under the Espionage Act - among very few who ever have been - but after it was revealed that the Ellsberg had been the subject of widespread and illegal wiretapping all charges were dismissed.

• Bradley Birkenfeld

Unlike the rest of the whistle blowers on or list, Birkenfield didn't cause problems for any governments around the world, but for one of the world's biggest financial companies UBS.

The 48-year-old American banker and whistleblower made disclosures to the IRS which led to a massive fraud investigation. In 2007 he gave information to the United States Department of Justice that resulted in $780 million in fines levied against UBS.

In 2008, Birkenfeld pleaded guilty to conspiracy to defraud the United States and was sentenced in 2009 to 40 months in prison. Many advocacy groups from around the world criticised Birkenfeld's prosecution and sentence.

Birkenfeld was released last year and September was awarded $104 million by the IRS for acting as a corporate whistleblower, the largest ever payout of its kind.

• Edward Snowden

And finally, the man of the moment. It is difficult to estimate Snowden's place in the history of whistleblowers as the full effect of his leaks is still to be seen.

However, considering the apparent scope of Prism and Snowden's own comments on the powers he had available to him, it is clear that this controversy is not going to disappear any time soon.

With Ellsberg claiming this as the most important leak in US history, Snowden's name is likely to appear on top whistleblowers list for some years to come.

As for what is going to happen to Snowden, that too is very unclear. The possibilities range from rendition to extradition; capture by Chinese authorities or even death at the hands of the Triads on orders from the US government - none of which, as Snowden admits, is very tempting to him.