I think Tom Riddle became Voldemort because he loved power and control. Growing up, he didn't have control over where he lived or what he did (at least, not much), so when he realized he could take control of his future he went power-hungry and completely overboard. He liked the idea that he could secure his future and his immortality by making horcruxes, and because he was so power-crazed, he ignored the consequences.

Voldemort, like Harry, had no prior knowledge that what he could do was actually magic. He had no idea there was a parallel world that existed alongside his own. So his ideas of mudbloods and muggles vs. wizards was not ingrained in him at birth. They were not a product of his upbringing, but rather a product of the idea of superiority that Salazar Slytherin had held. Finding out that he was in fact a descendent of Slytherin helped to solidify those ideas and his power trip. If Salazar Slytherin, an incredibly powerful wizard in his own right, had those ideas, then Tom Riddle's ideas were obviously right on target. And then he could not get the idea out of his head, and it grew monstrously until he became Lord Voldemort.

Regarding true historical figures who remind us of Voldemort, Hitler (the obvious choice) comes to mind. Another, lesser-known figure of history that comes to mind is Vlad Tepes III, or the historical "Dracula". Tepes lived in
15th Century Romania, specifically Wallachia (a region that borders Transylvania, where the legends of Dracula originate). He rose to power after his father sold him, as a teen, to Turkish lords to pay off a debt. He was a fierce and patriotic ruler, but he was also extremely cruel. Tepes used the method of impalement to teach his subjects a lesson about his rule. When all was said and done, he had eventually impaled a good 20,000 of his own subjects, purely because he was so power-hungry, and much of the time the only reasons he had for doing so were simply that he wanted to spread as much fear and "respect" as he could.