Tom Riddle Senior

"Within a few months of their runaway marriage, Tom Riddle reappeared at the manor house in Little Hangleton without his wife. The rumour flew around the neighbor­hood that he was talking of being 'hoodwinked' and 'taken in'... He left her, never saw her again, and never troubled to discover what became of his son."

- Albus Dumbledore on Tom Riddle

Tom Riddle Sr. (1905-1943) was an affluent Muggle who lived in the town of Little Hangleton. He was the son of the wealthy Muggle couple Thomas and Mary Riddle. Tom was married for a short time to Merope Gaunt and was the father of Tom Marvolo Riddle, also known as Lord Voldemort, who killed his father when he was sixteen in retaliation for Tom's abandonment of his wife and unborn child.

Early life
"She likes looking at that Muggle. Always in the garden when he passes, peering through the hedge at him, isn't she? And last night — hanging out of the window waiting for him to ride home, wasn't she?... I got him as he went by and he didn't look so pretty with hives all over him, did he, Merope?"

- Morfin Gaunt on Merope's infatuation with Tom Riddle

Tom Riddle Sr. lived in a luxurious manor house not far from a run-down cottage that was home to the Gaunts, a wizarding family descended from Salazar Slytherin and Cadmus Peverell. Merope, who led a miserable life of poverty and abuse at the hands of her father and brother, became infatuated with Tom, watching him ride by on his horse, sometimes in the company of a woman named Cecilia. Tom, on the other hand, mocked Merope and her family for their poverty and mental instability.

When her brother Morfin noticed her interest, he hexed Tom with hives. The Ministry of Magic discovered this, among other incidents, and presumably performed a Memory Charm on Tom. They also arrested Morfin and Marvolo Gaunt, and both wizards were sentenced to Azkaban. While they were gone, Merope made her play for Tom.

Marriage
It was speculated by Albus Dumbledore and Harry Potter that Merope used either the Imperius Curse or a Love Potion to attract him. In any case, the two married, despite public disapproval over "the squire's son running off with the tramp's daughter". At some point in their relationship, Merope became pregnant.

In any case, it is believed that Merope eventually stopped whatever enchantment she had used on Tom in the hopes that he had truly fallen in love with her since, or would at least remain with her for the sake of their unborn child.

Abandonment
"Tom Riddle left her while she was still pregnant... I believe that Merope, who was deeply in love with her husband, could not bear to continue enslaving him by magical means. I believe that she made the choice to stop giving him the potion. Perhaps, besotted as she was, she had convinced herself that he would by now have fallen in love with her in return. Perhaps she thought he would stay for the baby's sake. If so, she was wrong on both counts."

- Albus Dumbledore

Riddle reacted with shock and horror to the truth of his relationship with Merope, and fled back to Little Hangleton. He claimed to have been "taken in" by Merope, which may have been an allusion to her being a witch, or to her methods of attracting him. He did not state specifically that she used magic to seduce him, for the fear of being thought insane. Rumours in the town claimed that Merope had lied about being pregnant. Riddle's son himself came to believe that his father abandoned Merope solely because he discovered she was a witch.

Whatever the reason, Riddle abandoned his wife, and she was left impoverished, broken-hearted, and alone in London. Soon after, she gave birth to a son she named Tom Marvolo Riddle, after the baby's father and Merope's own father, Marvolo Gaunt. Merope died shortly after giving birth and the child was left in the care of a Muggle orphanage.

Death
In 1943, sixteen-year-old Tom Marvolo Riddle, who would later take on the alias Lord Voldemort, ventured to Little Hangleton to investigate his heritage. He learned the details of his parents' union from his uncle Morfin Gaunt and sought revenge on what he saw as the man who caused his mother's death. Tom Marvolo Riddle murdered his father and paternal grandparents with the Killing Curse and framed Morfin for the crime.

Tom Riddle Sr.'s murder was used by his son to transform Marvolo Gaunt's Ring into his second Horcrux. Voldemort seemed to see this murder as retribution for the miserable existence his father had condemened him to in his abandonment, as well as his own triumph over his "filthy Muggle" heritage. Voldemort made use of his father's murder again in 1995, when he used a bone from Tom Riddle Sr.'s grave to make the Potion that resurrected him.

Personality and Traits
Little is known about Tom Riddle Sr., but some things can be inferred. He seems to have been something of a snob and rather callous. For example, when he and Cecilia were riding by the Gaunt Shack on one occasion, Bob Ogden ran out, having been terrorized by the Gaunts, and stumbled into Riddle's horse. Both he and Cecilia "roared with laughter" at this. Very handsome and wealthy, Riddle boasted to his companion about how much property his family owned. Tom also abandoned his pregnant wife and apparently made no attempts to find out what happened to his child, likely out of indifference or ignorance of his son's continued survival, though the former seems more likely given that he had been made aware of Merope's pregnancy before abandoning her.

In fact, Tom was described to be more snobbish and rude than his parents, who were both very much that way as it is. This made Tom immensely unpopular in Little Hangleton, and the villagers were not at least sorry for their demise.

Appearances

 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Goblet of Fire 
 * Harry Potter and the Goblet of Fire (film) 
 * Harry Potter and the Half-Blood Prince 

Notes and references
Tom Jedusor Sr.