The issue with this kind of question is that "good natured" is really in the eye of the beholder, and extremely subjective. "Prosperity" is also a somewhat relative term. True, it can be generally measured by economic strength and trade, but some of the eras (regardless of whether they were democratic or dictatorial) of the most economic progress have been marked by extraordinarily high wealth inequality and powerful economic strength. Lastly, "ever" basically ensures that your question is unambiguously "yes" but isn't really helpful at all.

A few examples:

Lee Kuan Yew was the President (re: dictator) of Singapore. He ruled with an iron fist, but is particularly known for the sudden increase in Singapore's economy, so much so that Singapore developed into one of the "Asian tigers." (Along with Hong Kong, Taiwan, and South Korea, being the four new, small, powerhouses of the east Asian economy.)

In South Korea, Park Chung-hee played a similar role. He crushed his political enemies with ruthless abandon, flaunted workplace safety regulations, broke up unions, and flirted with establishing a Juche state in the South (similar to what they had in the North) until he was assasinated. Park is consistently ranked as Korea's #3 hero, right after King Sejong and Admiral Yi who compete for #1 and #2.

Speaking of King Sejong, he was the King of Joseon Korea in the 1400s. Under his reign was established the Hall of Worthies, a kind of science committee that developed solutions to problems that reformed the way Korea did basically everything, from taxation to musical annotation, and most famously, created a native alphabet for the Korean language called Hunminjeongum, which later evolved into modern Hangul. These reforms did wonders for the Korean economy, but as regards justice, law, and political freedom, King Sejong was hardly different from his predecessors or successors.

In my own area of expertise, Tibetan and Himlayan history, the Tibetan Emperors are most notable, especially Tri Song Detsen, who was Emperor over a militarily powerful, expansionist, and politically dominant Tibet. His armies struck deep into India and China, established rule over the Silk Route caravanserai, forced a peace treaty onto the T'ang Chinese, and oversaw the conversion of Tibet to Buddhism, in part at least, to turn the country to a religious system that matched the power of the economic strengths of China, India, and the city-states of the Silk Route.

Most of us learned of Chinggis Khaan and his government/descendants through the reports of their enemies. This was in large part on purpose. The Mongols wanted people to fear them as it made rebellions less likely, and cities often surrendered before the Mongol armies had to spend the time and energy in sacking them. That said, they were absolutely ruthless, punishing betrayal and rebellion with annihilation. But once the Khaans accepted a people as members of their horde, they became full members. When the Tatars rebelled, Chinggis Khaan had every male taller than the wheel of a cart executed. But to show that he wouldn't hold the descendants of the traitors responsible for their ancestors' crimes, he adopted several of the remaining Tatar children as his own. One of them became the "high judge" of the Mongol Uls. While there's all this focus on the war, death, and destruction brought by the Mongols, few remember that it was such a common saying that "a maiden could walk with an ingot of gold on her head and walk the Silk Route unmolested" that it's still a common expression in parts of the Himalaya to describe an era of peace and prosperity.

I feel like I could just go on and on giving examples. The thing is there's really no uniting feature. Democratic countries, such as the United States, have been brutal in the treatment of their indigenous population, of imported slaves, and their own working class, while still maintaining democratic governance (and restricting the participation of the aforementioned groups). France spent most a large portion of the 19th and 20th Centuries as a republic, but it was also the period of the largest and most violent expansion of the French Colonial Empire. As the British Empire commit horrible atrocities in Ireland, India, Australia, Africa, and... just about everywhere else, they were also experimenting with democratic governance in England, which grew with the rapid expansion of the industrial economy.

There are plenty of "good Kings" out in history. Especially when we expand our search to "ever." Even Gaddafi, someone I have no respect for and is definitely on the list of one of the worst modern dictators, oversaw the rapid rise of Libya's post-colonial economy, and had a personal charisma that was so inspirational that even after his death, people were still fighting in his name and claimed that he made them proud to by Libyan. There are very few instances where a good King was universally good. Or any country, regardless of political structure.

Edit: I'm not sure how to offer sources about these things at the moment, at least none that offer a good answer to the question at hand.