Salah Abdeslam is a 26-year-old French national who grew up in Brussels.
Police have said he played a key role in the planning and execution of the Paris attacks.
They believe he escorted the three suicide bombers who blew themselves up at the Stade de France and may have been due to carry out a suicide bombing himself, but for some reason did not go through with it.
Hours after the attacks on 13 November Abdeslam called friends in Belgium to drive to Paris to collect him, according to investigators.
Recently released security camera pictures showed him at a petrol station close to the Belgian border in northern France.
In those pictures he is seen with Hamza Attou, one of two men said to have driven him back to Belgium.
Their car was briefly stopped at the French-Belgian border and Abdeslam’s ID was checked, but at that time he was not on a wanted list and he was allowed to continue on.
He had been on the run ever since, holed up in various apartments, reportedly including the one police raided on Tuesday in Forest, a suburb of Brussels. His fingerprints were found on a glass there according to Belgian prosecutors. Two suspects escaped from that raid.