Black is the leader of a secret group of clones only known as Skull Squad. Only the best clones hand picked by Black from every legion may be apart of this group. The group does not answer to the Republic and doesn't follow their rules. They answer directly to the Jedi Council more specifically Masters Yoda and Windu. Jason himself wasnt born on Kamino. He was born on Corasaunt, the council found out he was forced sensitive. He was trained by Master Yoda till he reached the age of 25 when the Clone Wars broke out. Being one of the many people that believed Peacekeepers shouldn't lead the war he left the Jedi Order on good terms and told Yoda he would still serve the Jedi if they needed help. He then left for Kamino and was trained by ARC trooper Alpha, afterwards creating Skull Squad and offered their services to the Jedi willing to do missions that would be against the Jedi code and most Jedi would not do for moral reasons. They would be an unknown thorn in the Separatists side. He saw it fit and fair to learn both sides of the force and sought out the ancient home world of the Sith, Moraband. Finding old Sith texts and teaching, he taught himself the basics of the darkside, though vowing to never let himself fully turn and only using the darkside in dire situations (He is basically a Grey Jedi. If you don't know what that is, please look it up.) He doesn't like using the force during battles, he prefers his DC-15 blaster, but he has been known to use his yellow light saber. He and most of his squad would survive Order 66 and the Jedi Purge and went into hiding as Bounty Hunters as well as helping the Rebellion during the Galactic Civil War.
(What he looks like without his helmet/ His bounty hunter outfit for the Galactic Civil War)