The 523rd lgion was a batch of clones that were defective. They were put into service after that was found out. Commander Marks was the most defective and there leader. They were lead by Jedi bouny hunter Matt Shackleford. Eventuall after the Clone Wars the 523rd went renegade and took over many planets. They settled on Dagoba and were eventuall found again by there Jedi general.
Commander Marks was a clone of the Jedi Bounty HUnter Matt Shackford. He was defective and eventually died in battle against the empire alongside his best friend and general Matt Shackleford.
This group is dedicated in his memory. May he rest in peace!