WikiLeaks founder Julian Assange arrived at Britain's Supreme Court on Wednesday where he will ask to block his extradition to Sweden where he faces sex crime allegations.
The 40-year-old Australian begins his challenge before seven judges in the highest court in the land.
He is attempting to overturn a High Court ruling that it would not be unfair or unlawful to remove him.
A key legal question before the Supreme Court justices is whether a European Arrest Warrant (EAW) issued against him by a Swedish public prosecutor is valid under provisions of the 2003 Extradition Act.
The Swedish authorities want him to answer accusations of "raping" one woman and "sexually molesting and coercing" another in Stockholm in August 2010 while on a visit to give a lecture.
Assange, whose WikiLeaks website published a mass of leaked diplomatic cables that embarrassed several governments and international businesses, says the sex was consensual and the allegations against him are politically motivated.
The High Court upheld a ruling by District Judge Howard Riddle at Belmarsh Magistrates' Court, south London, that the computer expert should be extradited to face investigation.
Assange burst into the public consciousness in April 2010 when WikiLeaks released Collateral Murder — video footage of a US air crew shooting Iraqi civilians in 2007.
The whistleblower website, which claimed a database of 1.2 million documents within a year of its 2006 launch, regularly hit the headlines in 2010 with a series of leaks.
The U.S. Embassy Cables, Afghanistan war logs and Iraq war logs, which were drip-fed to the media in 2010, helped raise his profile.
By the end of the year he had become a minor celebrity.
Upon his arrest in December 2010 he had a number of famous friends and supporters who helped him to raise bail of 200,000 pounds, including film-maker Ken Loach and socialite and charity fundraiser Jemima Khan.
He has been on bail and living at the country mansion of a wealthy supporter in Norfolk.
If the Supreme Court rejects his appeal it will mark the end of his lengthy legal battle in the UK, but it will still be open to him to ask the European Court of Human Rights in Strasbourg to intervene on his behalf.