Today I present you: AU where Tom didn't get a letter from Hogwarts, because after WW 1 Magic Britain decided to cut ties with muggle Britain. So muggleborns are never contacted.
So Tom grows up thinking his magic is his superspecial unique power. He is not as refined as his canon counterpart, he didn't receive an education on his magic, but he is pure raw power and rage.
During WW 2 Tom gets shipped to war. Yes, he's still underage, but he's an orphan without any parental figure, so who cares?
Well, Tom becomes a war machine. His secret power translates in an incredible gut feeling. Also he is able to discern what he's being lied to. Also his magic protects him as a shield. And his raw power kills people from distance.
He looks like an incredible talented, lucky, brave, ruthless soldier, and he gets promotions and medals.
He also very much enjoys killing enemies and being praised for it. After the war, he decided to stay in the Army, the only place where he feels like his lack of morals and ruthless killing ability is welcomed instead of stunned.
He gets trained in strategy, combat, and so go on. He gets to go to university (he is fascinated by the atomic bomb).
He becomes a young, promising, handsome, intelligent, charismatic, soldier.
He never tells anyone about his superspecial ability. Snakes are his only friends.
And then Magic Britain after 10 years of peace decides to open up again.
So in 1956 Major Tom Riddle (of his grade is not possibile magic did it) discovers that
2- the magic world is spoiled and extravagant
3- the old-fashioned elite cares nothing for his success, he gets snubbed just for his birth
4- his raw power is impressive, but he lacks education.
Well. This stupid logic less medieval world which denied him his birthright won't know what hit it. They will kneel before a man like him.