Matthew Hopkins was the self-styled Witchfinder General, and a hunter of witches during the 17th century. (COMIC: Witch Hunt) Many witches hid from him in the village of Devil's End. (TV: The Dæmons)
He exposed a coven of witches in the village and had them burnt at the stake. (PROSE: The Eight Doctors)
In Chelmsford in 1645, Hopkins persecuted Matilda Brewer, who had become infected by the Skreeth, as he believed that she was a witch. Ace had seen a film about Hopkins in which he was played by Vincent Price. She noted that he actually resembled Price. (PROSE: The Devil Like a Bear)
As part of a prank, Miss Chief brought Hopkins into the 21st century, where he attacked the teachers at Coal Hill School in London. He found Clara Oswald, dressed as a witch, Miss Chief sent them back to the 17th century, where Hopkins threw Clara into the water to see if she floated. Miss Chief saved Clara, but Hopkins assumed she drowned and thus was innocent of witchcraft. When Clara tried stopping a woman called Agnes Leech from being framed as a witch, both Clara and Agnes were caught and put in solitary confinement in the dungeons. When the Twelfth Doctor came to rescue Clara, she accidentally named the Doctor as a witch, and both were to be executed. Miss Chief saved them from being hanged and brought them back to the 21st century, but returned them to the 17th century to retrieve to the TARDIS and free Agnes.
Bringing a cat called Smudge with her, Clara convinced the mob that Hopkins was a witch, and Smudge his familiar, but the Doctor prevented them from murdering Hopkins by sneakily putting Miss Chief's time travelling marotte in his belt, forcing Miss Chief to save his life. The Doctor believed that this was where the rumours where Hopkins was "swum" as a witch and drowned originated from. (COMIC: Witch Hunt)