Actually, his salary didn't amount to much in the early days so I imagine most of his investment capital came from his wife, who brought a fortune into the marriage. He acquired his first block of Coca-Cola stock in 1907 in lieu of a cash payment from the company for an endorsement deal. He acquired his United Motors (GM) stock in the same manner. His endorsement income was greater than his baseball salary for most of his career. And all the while he was making some deft plays in the commodity markets as well.True. He made a fortune speculating in Coca-Cola stock in the early twenties, but he got his initial bankroll to do it from the Detroit Tigers.
While being a ball player was certainly advantageous and marrying well didn't hurt, I think he displayed enough business acumen to become wealthy on his own account. He applied the same dogged determination to his business pursuits as he did to his play on the baseball diamond.
BTW, he left the bulk of his estate to his children so it says a lot about them if they chose not to attend his funeral while accepting their inheritance.