At some point scale will require you to hire, at least a few people, if you're really successful. But two examples that I can think of are Markus Frind (Plenty of Fish) and Markus Persson (Minecraft).
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Markus Frind is probably the biggest. He spent 5 years (2003-2008) working on Plenty of Fish, and at that point it was bringing in about $5M/yr and had 3 employees.
When the site sold in 2015 for $575 million it was 70 employees, but he still owned 100% of the company.
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Markus Persson would be another possible option, for the first $10-20M that Minecraft brought in he was the only person (aside from a contracted musician). And then for a while after that, it was him and his friend who was hired to manage the business side so he could focus on the programming work.