During the First Battle of Kamino, we see Alpha-class ARC troopers.
The Alpha-class Advanced Recon Commandos, also known as Alpha ARCS or simply Alphas, represented a group of 100 Advanced Recon Commandos. These soldiers were created using the genetic material of Jango Fett by the Kaminoans on the planet Kamino. These ARCs would serve the Republic within the Special Operations Brigade of the Grand Army.
The development of the Alpha-class ARC troopers occurred after the creation of the Null-class Advanced Recon Commandos. The existence of the Null-class was a carefully guarded secret by the Kaminoans. The experiences and knowledge gained from producing the Null ARCs significantly aided in the refinement of the Alpha ARCs.
After the Kaminoans had nurtured and trained the Alpha ARCs under the direct guidance of Jango, they were unaware that Fett had secretly programmed personal directives into each of them. One such directive was the order to eliminate all younger clones should Kamino ever fall under the control of the Confederacy of Independent Systems. During the First Battle of Kamino, Alpha-17 almost executed this order, but the Galactic Republic successfully defended the planet.
Similar to their Null-class predecessors, the Alpha-class ARCs were designed with unaltered, independent minds. However, these second-generation ARCs displayed greater obedience and reliability towards the Jedi due to Jango's specific instructions for them to follow orders. Despite this, the ARCs were not hesitant to express their disagreements or opinions regarding a Jedi's orders if they perceived them as incompetent or lacking sufficient strategic planning.
During the Clone Wars, a palpable rivalry existed between the Null-class and Alpha-class ARCs. While the Alpha-ARCs naturally inherited Jango's inclination towards solitude, they also possessed a sense of pride in being part of a formidable military force. Furthermore, they held a high regard for the combat and leadership abilities demonstrated by nearly all Jedi. The Alpha ARCs viewed the Nulls' open disregard for Jedi and Republic authority as an affront to the entire clone army. While most Alpha ARCs were primarily loyal to the Galactic Republic and, to some extent, followed the Jedi's leadership, the Null ARCs pledged their allegiance solely to Kal Skirata. Consequently, the Alpha ARC troopers considered the Nulls to be rogue clones and a disgrace to Jango Fett's legacy.
When Supreme Chancellor Palpatine initiated Order 66, not all Alpha ARCs complied with the command. While some chose to obey the Chancellor's directive, many others defied Palpatine due to their unaltered independent thinking and the close relationships they had formed with the Jedi during the Clone Wars. Some Alpha-class ARC troopers chose to retire on Coruscant or Kamino, becoming instructors at the Empire's recruitment facilities. Others emulated Jango Fett by becoming bounty hunters. Still others decided to join the Alliance to Restore the Republic.