• Tea Party activist was plaintiff in landmark case against NSA• Notoriously litigious, he sued Clinton administration 18 times• Klayman is a former prosecutor for the US Justice Department• Larry Klayman in his own words: why I challenged the NSA in court

He is the staunchly conservative lawyer, Tea Party activist and self-proclaimed inspiration for a character from the West Wing who landed the first judicial blow against the National Security Agency, an achievement celebrated by civil libertarians across the country.

Larry Klayman, the 62-year-old lead plaintiff in a landmark case against the National Security Agency, was thrust into the spotlight on Monday after a federal judge ruled that the mass collection of phone record data – the subject of his lawsuit – was probably unconstitutional.

His penchant for lawsuits has seen him take on targets as varied as Hugo Chávez, Bill and Hillary Clinton, Dick Cheney, Barack Obama, Mark Zuckerberg and, in a lesser-known case, his own mother.

He is often referred to as a “gadfly”, which is probably an understatement for a former Justice Department prosecutor who switched sides before filing at least 18 suits against the Clinton administration in the 1990s. He was once barred from a California courtroom for, among other impertinences, "making further argumentation when he had been ordered by the court to cease speaking". Characteristically, Klayman appealed.

But Klayman's lawsuit against the NSA is unlikely to make him a hero among surveillance sceptics on the left.

Among his many political obsessions, Klayman is a so-called “birther”, who claims that Obama was born outside the US and is therefore ineligible to be president.

Klayman recently said Obama was a Muslim with an “apparent allegiance to sharia law”, and asked aloud whether the president might be overthrown in a coup. Although he claims to be non-partisan, and simply wants to take on powerful elites regardless of their political affiliation, Klayman once ran an unsuccessful bid to be a Republican US senator, receiving just 1% of the vote in the Florida primary in 2004.

He has written three books, two of which are entitled Whores, and has founded two trenchantly conservative groups: Judicial Watch and Freedom Watch.

Klayman fell out with – and then, predictably enough, sued – Judicial Watch. But he remains involved with the Freedom Watch website, where his biography includes a link to an article in which he is described as “the one-man Tea Party”. The same page also links to video clips from The West Wing, which feature an irritatingly persistent lawyer called Harry Klaypool. Klayman believes the character – a thorn in the side of the White House – is based on him.

That is a not an implausible assumption, given the long line of controversies Klayman has ignited through his endless courtroom battles, a career that has earned him the nickname "Litigious Larry". Until now, the Clintons, who he accused of numerous abuses of office, have been his most notorious adversaries.

In 1998, when a piece emerged in Newsweek revealing that Klayman was suing his mother over $50,000 he had spent on nursing costs for his late grandmother, he did not deny the case, but said it was “obviously dug up by private investigators of the Clintons” to smear him.

Of course, Klayman’s eccentric professional life should have no bearing on his NSA lawsuit. Monday’s ruling, in which Judge Richard Leon described that the mass collection of phone data was “almost Orwellian”, will now be subject to appeal by the government.

Klayman is just one of several plaintiffs, and any appeal will focus exclusively on the merits of the case – not the political views of those bringing it. Besides, similar lawsuits are being brought by the American Civil Liberties Union and Electronic Frontier Foundation, both reputedly liberal organisations.

But outside of the courtroom, Klayman's controversial background and radical beliefs, particularly over Obama's religion and birthplace, are likely to influence how he is perceived.

In an article published on September 11, Klayman wrote of Obama:

It is time that we Christians, Jews, people of faith and all true patriots say: enough is enough, and ourselves, in a very real way, "Occupy Washington" to cleanse the nation of the half-Muslim, anti-white, socialist fraud in the White House before the nation goes under for the final count.”

In the same piece, Klayman said that if the president was convicted for voter fraud, millions of Americans should amass in Washington to demand his overthrow. “If the Egyptians can do this with regard to another radical Muslim, former president Mohamed Morsi of the Muslim Brotherhood, then can't we Americans do it with Obama?”

It was a call to action Klayman repeated during a Tea Party rally over the government shutdown the following month, when he said the country was “ruled by a president who bows down to Allah”. “I call upon all of you to wage a second American non-violent revolution, to use civil disobedience, and to demand that this president leave town, to get up, to put the Qur'an down, to get up off his knees, and to figuratively come up with his hands out,” he said.

Confronted over the incident by MSNBC host Martin Bashir, Klayman said his remarks had been taken out of context and were “metaphoric”.