Jack Reyes is a skilled bounty hunter that seperated himself from other hunters by taking jobs that required him to target Jedi Knights.
All of his Jedi-hunting jobs he took from an employer that he would never name - even for a reduced prison sentence. It is suspected that it is mostly a kind of bounty hunter "honor" thing, where a hunter should never reveal his client. Some others suspect that if he did reveal the identify of his employer, his life would instantly be forfeit.
While active as a bounty hunter and under the employ of the mysterious company, Reyes took down a total number of five Jedi Knights.
He used an advanced, highly-modified sniper rifle to do the job. The rifle was designed with a larger clip and the ability to fire much faster than most sniper rifles - a necessary thing when targeting the danger-sensing Jedi. In the event that a Jedi would get too close to him, he used a powerful shot guns filled with high dispersal ammunition, which prevented the Jedi from simply deflecting the projectiles with their lightsabers.
Jack was eight years into a 50 year prison sentence in the Reticulli System when Captain Rick Nutron raided the prison and brought him aboard.