Tom Riddle's mother was a squib(Born as pure blood having no magical powers)

Merope Gaunt, Tom Riddle's mother, was indeed a squib - born into the pure-blood Gaunt family (descendants of Slytherin) but showing no magical ability herself. This shamed her family deeply. She used a love potion to enchant Tom Riddle Sr., a Muggle, and when she stopped giving him the potion and became pregnant, he abandoned her. She died giving birth to Tom Marvolo Riddle, who would become Voldemort.