Hardwin Potter was an early wizarding ancestor of Harry Potter. His primary significance in Wizarding History stems from his marriage to Iolanthe Peverell, through which the Invisibility Cloak of Ignotus Peverell was passed into the Potter Family. This union established the lineage that would eventually lead to the cloak being inherited by Harry Potter centuries later. All known information about Hardwin Potter comes from supplementary material written by J.K. Rowling. (Pottermore)
Living in the 12th century, Hardwin Potter was a member of the Potter family which, at the time, resided in the West of England. (Pottermore) He married Iolanthe Peverell, a young Witch from the village of Godric's Hollow and the granddaughter of Ignotus Peverell. As the Peverell male line had died out, Iolanthe, being the eldest of her generation, inherited her grandfather's famed Invisibility Cloak. Upon their marriage, Hardwin respected the tradition of secrecy surrounding the Cloak's true nature as one of the Deathly Hallows. He and Iolanthe established the Potter family tradition of handing down the Invisibility Cloak to the eldest descendant of each new generation, a practice that continued for centuries. (Pottermore)
There is no canonical information regarding the physical appearance or personality traits of Hardwin Potter.
While he was a Wizard, no details regarding Hardwin's specific magical abilities, skills, or Wand are known. (Pottermore)
Hardwin Potter is not mentioned in the original seven Harry Potter novels. His existence and entire backstory were revealed by J.K. Rowling in an essay titled “The Potter Family,” originally published on the Pottermore website (now part of Wizarding World). This essay provided the official explanation for how the Invisibility Cloak, one of the Deathly Hallows, became a Potter family heirloom, a detail not explicitly explained in the books.