In our long running epic game, the party cleric Caemon started out small: he invested in a few things, started an oyster farm(?!), and started his own bank. After a few years (real time) he was known as the richest man in the world. It got to the point where he controlled the economy of the entire kingdom his businesses were based in.
Unfortunately, that kingdom happened to be
mine.
Subtle power struggles ensued, political maneuvering, lots of intrigue. It's not that we weren't friends; he was the high priest of Jas, the god of Good and the sunrise, and I was Malachi the ranger, founder and first king of Falcor (Malachi was very Chaotic and chafed under his crown, and by the end he was the 1st, 3rd, 5th, and 7th king of Falcor

), and by that point in our careers had become kind of a direct mortal agent of our god. (Jas had been raised to divinity from human origins, and as such was kind of a "hands on" type of god in a very Eddings kind of way. He even visited from time to time, and would bring Malachi boxes of his favorite cigars [Malachi was very much a character in the vein of Nick Fury and Wolverine])
Anywho, Caemon pretty much owned the economy of Falcor and had so many businesses I couldn't count them. He ran the banking system (actually he owned it, Malachi was Chaotic Good and felt the only interference he should have in people's lives was to provide military protection, so he didnt touch the economy.) But as High Piest of the state religion he also ran the Church and all it's charities. His stated goal was to make everyone in Falcor rich. And he did so. The only problem was that while everyone had lots of money, inflation went crazy and loaves of bread started costing 15 gold pieces. Caemon and Malachi had power struggles of a sort, which ended up with Malachi gettin sick of everything and abdicating in favor of Caemon and taking off into the wilderness for a year. Then Jas visited me and told me I shouldnt have handed Caemon the throne, it was my country. So I went back and told Caemon that Jas had commanded me to take back the kingdom. He left in a huff, and never even bothered to commune with Jas to see if I had told the truth. I had in fact lied.
He eventually moved to a new continent to found a new kingdom, a theocratic utopian society where no one needed money and everything was provided for by the church. Funded by his business activities on the mainland.
His player had notebooks full of data and accounting stuff. He had a lot of fun with it
Damn, I miss that game. We did that for 12 or 13 years. At the end, half the ganme sessions were political or economic, almost all roleplaying; diplomatic meetings, balls, sometimes wars. It took something momentous to get us out in the field again. We almost fought the god of entropy and Evil once.