This is really a theory that I turned into a fic. In earlier versions where JKR had written that Voldemort was the last remaining ancestor of Salazar Slytherin, this had been 'corrected' to descendant. However she then hinted that the word ancestor had been out there deliberately, and it was put back in in later versions.

TOM RIDDLE AND THE UNUSUAL HAT

Woldemorre was a man. He was born in 13BC, and had something of an empire.

He was widely known for torturing those who were not magical. He called them Mulgers.

Woldemorre was afraid of death, and preserved his mind in a hat, where it would lay dormant until a suitable person took it upon themselves to wear the hat. Many preservation spells were laid upon the hat to be sure it stood the test of time. After all, there were not many minds that could contain the destructive force of Woldemorre without imploding.

He had three children, each by a different wife. Two were boys. One was killed in a fight, a fight of raw magic that caused great destruction. The other shunned the evil ways of his father and lived in the non magical community quite happily.

The third child was a girl and she married a warlock by the name of Slytherin.

13th June, 986

"What is it exactly you're looking for?" Rowena said, absently digging through the piles of clothes the toothless old woman had to sell.

"A hat. I told you." Godric replied, casting aside an unravelling jumper.

"Here's one!" Rowena said, holding up a brown cotton one. Godric glanced at it and shook his head. Rowena rolled her eyes and sat obstinately on the ground.

"Aha!" Godric said, pulling a battered black pointy hat from the pile. "Perfect!"

"Good for you. Now can we please get back to the others?"

The toothless woman came forward. "Gole gall-yon" she mumbled, holding out her hand. Godric paid and jammed the hat on his head.

"Doesn't suit you. Really." Rowena remarked. Godric shrugged. "I like it." The strange urgency that had gripped him when he saw the clothes stall had left him.

Suddenly he stopped, and his eyes went slightly blank. Rowena went a few steps forward, then realised he wasn't with her. She went back.

"You right?" she asked. Godric suddenly came back. "Fine. I'm fine."

4th December, 1059

The school was quiet, the children sleeping. Two of the four, no longer young and sprightly, but old and withered, sat on the floor next to a bed. The bed contained the third of them. Salazar had left them only a few months before.

Helga lay in a fitful sleep, her yellow and white hair wispy on the pillow. Rowena and Godric had stayed with her all through the fever, relying on others to keep the school in working order.

"How... how much longer?" Rowena whispered. Godric didn't answer for a few moments, then said "She won't last the night."

A grimace covered Rowena's face. "Mary should be here." Mary was the child of Salazar and Helga, and was sixty four now. She had gone to Africa thirty years ago to become a witch doctor. They had not heard from her since.

Salazar's departure had crushed Helga. She had fallen ill a month before, but in the time after he left she had not seemed to know herself. She didn't turn up to teach her students, and simply sat in her room doing nothing. She hardly ate, hardly slept. And then the fever came.

"First Salazar goes, now... now Helga is too. How long are we going to last after this. What will the school do?"

"We have competent teachers. Aidan will make a good head when the time comes."

"But how can he sort them? No doubt he will manage to cock it up in some way, putting Gryffindors with Hufflepuffs and soforth. And what of when he is dead and buried? How can a person who never even knew us sort them?"

"We could leave.... a device. Something to do the job for them. But how, what?" Godric wondered. In the flickering candlelight, the black pointed hat seemed to be park of his head, the shadows masking the brim.

Godric lifted his hand to his forehead, but touched instead the fabric of the hat. Slowly, he drew it off.

Rowena looked at him, puzzled. Then it dawned on her too, and the enlightenment showed in her face. Godric nodded, but then Rowena shook her head.

"Too late. Salazar is gone from us and Helga is dying. We cannot enchant with only two people."

"Helga isn't dead yet. As for Salazar, neither is he."

"Helga is not in a fit state to do anything of the sort!"

"There is a way.... Godric said. "There is the practice of taking a small part of the life essence and improvising it in place of the person itself.

"Helga hardly has life to spare, Godric!"

"She will die anyway!" he said, a tear forcing itself out of the corner of his eye. "What is a few hours? Can you not see how she is suffering, and how we need this?"

Rowena cast her eyes to the ground. "Very well." she whispered.

The moment Godric laid the tip of his wand on her forehead and took the red strands that were life, Helga lay still. His hand shook, but still he managed to act as Helga and give the hat some of her mind. Then he and Rowena gave it their essence too.

The next day, they looked all over the castle for something that best described Salazar. They used an amulet he had somehow forgotten to take with him. Neither of them expected it to work, but it did. The hat absorbed it readily, and so was completed. It was almost as if there was something about him that the hat recognised.

September 1st, 1937

Tom Riddle had always been alone.

In the orphanage where he lived, he was isolated. He had long ago pushed his bed against the wall, as far away from the others as he could get it.

He often wondered about his father. The mysterious muggle who had deserted his mother as soon as he realised she was a witch. Tom had never understood how she could still have loved him so much after that. He had left before he even found out he had a son.

Tom had one picture of his mother. It was blurry and monochrome, but it was still his mother smiling at him from the paper. It was crumpled, grubby from all the times he'd fingered it and it was easily his most prized possession.

He had been very happy when his letter came. He thought that perhaps now his life would take a turn for the better.

The train journey had been uneventful. He had simply sat in a compartment with three other first years, and watched as gradually they broke the ice between each other, began talking, became friends, sharing pasts. Now and then one of them had tried to include him in the conversation, but Tom had given short, clipped answers to the questions they asked, even though he had wanted desperately to be included with them, to be their friends. Eventually they had dismissed him as being cold and awkward.

Now, standing in line to be sorted, Tom was tense. Being in a muggle orphanage, he didn't know or carewhat each house entailed. He simply wanted to belong to something.

His name was finally called, and he stepped forwards to be sorted into the house that would be his family for the next seven years.

He lowered the hat over his eyes, and it spoke to him.

"Ah yes, good memory here. You're very loyal, what's this? You still feel loyal towards a man you never even met. Not afraid of hard work either, are you? Yes, there's no question that you should be in -"

The hat suddenly stopped talking. Something in Tom had awakened the two thousand year old spirit that had resided in the fabric, that which had seen so many young minds and dismissed them all.

Beating the collective minds of the founders out of the way, it slipped into the passage into the mind they had created, and instead of simply gazing down it, it wormed its way into Tom's mind.

Free at last from the spirit, the hat went back to sorting as if nothing had happened. But now something had changed about the boy. He now possessed all the qualities of a Slytherin, and these overshadowed the Hufflepuff ones in a big way, even if he was a half blood.

"SLYTHERIN!" The hat screamed, and Tom left the stool and went over to the Slytherin table, feeling somehow heavier than he had before.

For the first few days in his new house, Tom did not get on well at all with the people in his house, but then it started to get easier. He began to see their point of view when they spoke with venom about the muggles and mudbloods.

The spirit of Woldemorre was slowly but surely taking over. Every night Tom dreamed of places that seemed so real, not like the places created in a dream, but places that could be real, even though he had never seen them before. He didn't know that they were not dreams but memories from someone else's life. He found he excelled in lessons, not knowing it was because he shared his brain with someone who had done it all before.

He had been there for two months when it first happened. He had an itch on the back of his neck, but was trying not to scratch it - a test of willpower. Finally, he gave in and tried to move his hand to scratch.

But he couldn't.

For about five seconds his hand lay on his lap motionless, before Woldemorre's strength gave out and the hand returned to Tom's control.

But from then onwards it became a downhill struggle. Two months after that first event, Woldemorre had regained enough strength to suppress Tom about half of the time. It was very unfortunate that around the same time Tom realised that he really did have a very serious problem and needed to tell someone, Woldemorre became strong enough to prevent him doing so. Tom would get up and walk off with intent to tell someone, and then Woldemorre would force his to turn around and go back. Half the time it was Tom walking and talking, and the other half of the time it was Woldemorre. Sometimes strange noises would come from Tom's mouth as both minds tried to say something different at the same time. People began to ask questions, was the boy going mad, what was wrong with him. But then Woldemorre gained the upper hand, the "madness" subsided, and Tom was seen as everyone as back to normal.

Two months later, it was Tom who only occasionally managed to prevent Woldemorre from moving his hands. He became a prisoner in his own body. He saw everything, tasted everything, felt everything. But he chose to do none of it.

Woldemorre had learned of a secret chamber created by his probable descendant Slytherin, and had begun searching for it. He was still searching two years later, when he created a name for himself, basing it mostly on his own name of Woldemorre, but adding a silent T on the end and changing the W to a V. It fitted rather well with Tom's name, I am Lord Voldemort being an anagram of Tom Marvolo Riddle. Voldemort was a product of both Woldemorre and Tom Riddle.

By fifth year, when he finally found the chamber, the spirit of Tom had withered to a tiny wisp, hardly there. Still, he had imprinted on Woldemorre, who had involuntarily taken parts of Tom and mutated them. Tom's strange loyalty towards the man who had abandoned his mother had been replaced with a burning hatred.

When Voldemort left school, both seventeen and one thousand nine hundred and fifty seven, he began mutating himself in his quest for immortality. He had left something of himself when he was sixteen, in a diary, but that was only ever meant to be a temporary thing, to carry on the mudblood purging after he had left. If he were to do the same thing as before, invest his whole essence in a single object and wait for a subject to come along and take his entire mind inside their own, it would probably take all of infinity. Only after around two thousand years had someone come along who could support two whole minds, how long would he have to wait until one came along who could support three? He and Tom had become so tightly joined that Tom would have to be brought along as well.

Immortality would have to be brought about by mutating himself. There were new procedures now, that hadn't been around two thousand years ago.

This time around he would get it right. This time around people would hear his name and shudder.