Tom Riddle wasn't a hero. He was a villain whose villainous plot was to create a fake villain named Voldemort for him to defeat. He arranged for there to be a kidnapping attempt on the daughter of the minister of magic so that he could save her and be propelled into herodom. But things did not go according to plan:

"Long ago, long before your time or Harry Potter's, there was a man who was hailed as a savior. The destined scion, such a one as anyone would recognize from tales, wielding justice and vengeance like twin wands against his dreadful nemesis." Professor Quirrell gave a soft, bitter laugh, looking up at the night sky. "Do you know, Miss Granger, at that time I thought myself already cynical, and yet... well."

The silence stretched, in the cold and the night.

"In all honesty," said Professor Quirrell, looking up at the stars, "I still don't understand it. They should have known that their lives depended on that man's success. And yet it was as if they tried to do everything they could to make his life unpleasant. To throw every possible obstacle into his way. I was not naive, Miss Granger, I did not expect the power-holders to align themselves with me so quickly - not without something in it for themselves. But their power, too, was threatened; and so I was shocked how they seemed content to step back, and leave to that man all burdens of responsibility. They sneered at his performance, remarking among themselves how they would do better in his place, though they did not condescend to step forward." Professor Quirrell shook his head as though in bemusement. "And it was the strangest thing - the Dark Wizard, that man's dread nemesis - why, those who served him leapt eagerly to their tasks. The Dark Wizard grew crueler toward his followers, and they followed him all the more. Men fought for the chance to serve him, even as those whose lives depended on that other man made free to render his life difficult... I could not understand it, Miss Granger." Professor Quirrell's face was in shadow, as he looked upward. "Perhaps, by taking on himself the curse of action, that man removed it from all others? Was that why others felt free to hinder his battle against the Dark Wizard who would have enslaved them all? I still do not understand even now. My cynicism fails me, and I am left silent. But there came a time when that man realized he might do better fighting the Dark Wizard alone, as with such followers at his back."

"So -" Hermione's voice sounded strange in the night. "You left your friends behind where they'd be safe, and tried to attack the Dark Wizard all by yourself?"

"Why, no," said Professor Quirrell. "I stopped trying to be a hero, and went off to do something else I found more pleasant."

At this point, he decided to go full-time as the fake villain persona, and did so for the next eight years, when he decided to abandon it.