Unfortunately, the brilliance that Bathilda exhibited earlier in her life has now dimmed. “The fire’s lit, but the cauldron’s empty," as Ivor Dillons put it to me, or, in Enid Smeek’s slightly earthier phrase, “She’s nutty as squirrel poo.”
—excerpt from The Life and Lies of Albus Dumbledore, by Rita Skeeter (DH18)
Bathilda Bagshot was a famous magical historian and author of one of Hogwarts’ standard textbooks, A History of Magic. Her book is one of the books Hermione chose to store in her small pouch with the magically enlarged interior, in case it might prove useful during the quest to find and destroy Voldemort’s Horcruxes (DH16).
Much of what we know about Bathilda Bagshot is from highly questionable sources: the sensational Rita Skeeter expose-like book, The Life and Lies of Albus Dumbledore (DH18), the narrative about Albus Dumbledore’s years in Godric’s Hollow offered by the skeptical Great Auntie Muriel at the wedding of Bill Weasley and Fleur Delacour (DH8), and from Bathilda’s posthumous encounter with Harry, Ron and Hermione, while her dead body was being physically inhabited by Voldemort’s snake and Horcrux, Nagini (DH16).
We do not know where she spent her early life, but Bathilda Bagshot was already living Godric’s Hollow as an adult when young Albus Dumbledore and his family arrived there. Kendra Dumbledore arrived in Godric’s Hollow with her children c. 1850, after the imprisonment of Albus Dumbledore’s father, Percival, for the murder of three young Muggles who had tormented Albus’ sister, Ariana, an event which occurred “scarcely a year” before Albus Dumbledore’s first year as a Hogwarts student (DH2, 8). According to Rita Skeeter’s expose-like book, The Life and Lies of Albus Dumbledore, Bathilda tried to befriend Kendra Dumbledore after they arrived, but she was rebuffed.
Nevertheless, Bathilda became good friends with young Albus Dumbledore, whom she perhaps had come to regard as a protégé, being impressed with a paper he wrote as a Hogwarts student for the scholarly journal, Transfiguration Today (DH18). Rita Skeeter learned of their close friendship and was so keen to have Bathilda as a source for her screed on Dumbledore, she admitted using Veritaserum on Bathilda to get the information she wanted (DH18). Bathilda’s care and concern for young Albus was such that, when she took in her great nephew, Gellert Grindelwald, after his expulsion from Durmstrang, Bathilda made a point of introducing Grindelwald to Albus, who she believed was “missing the company of lads his own age” (DH18).
Later in her life, Bathilda befriended James and Lily Potter, and “dropped in most days” to see the young family, regaling them with stories of Dumbledore’s youth. Bathilda was the only person to join James and Lily for Harry’s birthday tea when Harry turned one year old (DH10).
Bathilda was murdered by Lord Voldemort or Nagini sometime in the weeks before Christmas Eve, 1997. When Harry and Hermione visited Godric’s Hollow Christmas Eve, 1997, and were accosted by who appeared to be Bathilda Bagshot, it was really Nagini inhabiting Bathilda’s dead body (DH17). Bathilda’s body was discovered several months later, shortly before the March, 1998 broadcast of the underground radio program “Potterwatch,” which reported the discovery (DH22).
Gellert Grindelwald is her great-nephew (DH18).
Writing, a brilliant pre-20th century historian
The French Saint Bathilde was a runaway slave who married King Clovis II and died in 680 (Catholic Encyclopedia).
'Bagshot' is the name of a village in Surrey, England. Could also come from 'Robin of Bagshot,' a character in the 1728 play "The Beggar's Opera." Bagshot was a scoundrel with many aliases (Brewer's Dictionary).
Most likely, the name 'Bathilda Bagshot' was simply meant to hint that she was a "batty old bag."