Saul is good guy turned bad by a magical staff in Shadowgate 64: Trials of the Four Towers. It started when he and his friend, Lucas, went out in search of gold and gems. While they were digging, they came across a staff. They believed it was the same staff used by the famous Lord Jair. According to Lucas, the staff started to make Saul "half-mad" and when Lucas tried to talk Saul out of something, he killed Lucas and ran off with the staff. He then headed back home where his mom, Jezibel, noticed he had a dead look in his eyes. He then left with a dwarf and never came back. His mom died a fortnight later from the black death. After leaving his mom's home, he headed out and became an assistant of the evil leader, Belzar. However, when the main character, Del Cottonwood, approaches him wearing Jezibel's pendant and tells her that she died, he instantly regrets his decisions and decides to turn good again. He then proceeds to allow Del access to the Chamber of Holding while he goes to take care of the other guards.
It isn't clear what happens to Saul. If you leave the Chamber of Holding before reviving the Warlock Lord, he and the other guards have disappeared. However, talking to Jezibel or Lucas will cause them to acknowledge the fact that he changed his ways.