The behind the bastards show about him goes into some detail about his early life. Iirc, he was an unremarkable investment worker (not particularly successful or unsuccessful) but somehow managed to become the personal investor for a billionaire and then a little while later he has billions of his own.

My guess is the money came from his first forays into the sex provider and blackmailer business with that first boss or maybe his whole social circle, but obviously there isn’t much about this on public record.