Whistleblowers have been impacting history for years. While many choose to remain anonymous, other whistleblowers make their identity public.

In recent times, NSA leaker Edward Snowden and WikiLeaks founder Julian Assange have been popular whistleblowers. While Snowden has taken refuge in Russia, Assange has been living in the Ecuadorean embassy in London for nearly five years. The two could still be imprisoned if they are caught.

Several whistleblowers have been imprisoned for leaking classified information, such as Israeli nuclear whistleblower Mordechai Vanunu and WikiLeaks source Chelsea Manning. However, Manning was released May 17 after serving seven years of a 35 year prison sentence.

Here is a look at some famous whistleblowers:

Mark Felt

The former second associate director of the FBI, Mark Felt revealed himself as “Deep Throat” three decades after he helped Washington Post reporters, Bob Woodward and Carl Bernstein reveal the Watergate Scandal in the early 1970s that forced President Richard Nixon to resign.

Chelsea Manning

Manning was charged with indirectly helping enemy forces by leaking several classified material to WikiLeaks. Her 35-year prison sentence was cut short by former President Barack Obama, who granted her clemency. She walked free from Fort Leavenworth military prison in Kansas last Wednesday.

Daniel Ellsberg

The former U.S. military analyst, while employed by the RAND Corporation, leaked the Pentagon Papers in 1971 to the New York Times and other newspapers. The documents were a top-secret Pentagon study of U.S. government decision-making in connection to the Vietnam War.

Julian Assange

Assange is responsible for releasing over 1.2 million leaks till date since the website’s creation in 2006. He could face trial in the U.S. for releasing classified information. On May 19, Sweden's director of public prosecutions dropped a rape investigation against Assange. However, his arrest warrant in London still stands.

Aaron Swartz

Swartz, who was born in Illinois, hacked into academic journal database JSTOR and downloaded more than four million articles through the Massachusetts Institute of Technology’s computer network in late 2010 and early 2011. Unlike other whistleblowers who leaked classified government documents, Swartz leaked scholarly articles, which could be accessed through JSTOR subscription.

In 2011, he was arrested by MIT campus police and faced several charges, including up to $1 million in fines and 50 years in prison. In January 2013, he was found hanged in his Brooklyn apartment. His family and friends accused the government of driving Swartz to suicide. One week after his death, WikiLeaks tweeted saying Swartz was in touch with Julian Assange from 2010 to 2011. WikiLeaks also said he was their source at one point.

Sherron Watkins

Sherron Watkins, who was Vice-President of Corporate Development at Enron Corporation, was the woman behind exposing one of the largest accounting frauds in U.S. history. The leak led to the company’s CEO Jeff Skilling’s 24-year prison sentence.

Frank Serpico

Frank Serpico, who is the former New York City police detective, revealed widespread corruption and bribery within his police department in the early 1970s.

Jeffrey S. Wigand

Wignad, who was a research scientist at tobacco company Brown & Williamson, was the first major tobacco whistleblower to expose that cigarette companies knowingly tried to use more nicotine.