As your character earns enough XP and gains sufficient level doesn’t it make sense that he’d start to attract some followers? Your character is a role-model for aspiring heroes. Tales of his exploits and successes will eventually reach the ears of impressionable youngsters. Inevitably some of them will take steps to seek out your character and bask in his greatness. Whether they seek to learn from him directly or they just want to be close by the next time something awesome happens, your PC has made a name for himself and gaining henchmen is one of the consequences of his fame.
Your character’s ever-developing reputation is a big part of what defines the PC and is just as big a part of how other people will interact with him. But we’ve already written about Reputation (Part 1 | Part 2 | Part 3) so we won’t bother retreading over that ground again. Instead I want to look at the idea of PCs attracting henchmen of their own.