I believe "good tyrant" is a contradiction in terms. By definition a tyrant rules cruelly, unjustly, and oppressively. There is no good to be had from that.

However, their have been benevolent dictators. This is off the top of my head, but in around the 4th Century BC, Rome abandoned their consular form of government because they were being attacked by three neighboring tribes. Roman law allowed a Dictator to be appointed in time of war.A farmer, at the time, Cinncinatus, was called upon to be this dictator. These wars lasted about 20 years, and at their end,Cinncinatus immediately resigned as dictator. He did not attempt like many dictators, to consolidate his power and remain dictator after the war. He was also known for his kind treatment of all Romans, without regard to their class, during his reign as dictator.

I hope this helps.