Bellatrix, her husband, and her brother-in-law, were active Death Eaters during Voldemort's rise to power, and evaded capture and suspicion until after the Dark Lord's downfall.

In this book, Rowling used Albus Dumbledore's Pensieve as a plot device to reveal that Bellatrix, rather than deserting her leader like many other Death Eaters, was part of the group of dark wizards – along with Rodolphus, Rabastan, and Barty Crouch Jr – that tortured well-known aurors Frank and Alice Longbottom in an attempt to gain information about Voldemort's location.

After escaping from prison, she was present at the Battle of the Department of Mysteries in the climax of the book, in which a group of Death Eaters attempted to steal Sybill Trelawney's prophecy pertaining to Voldemort's downfall.

Rowling let Bellatrix prove her magical prowess during the mission when she overpowered her niece Tonks and Kingsley Shacklebolt in one-on-one duels, killed her cousin Sirius by blasting him through the veil in the Death Chamber, and deflected one of Dumbledore's spells as she made her escape.

At the beginning of Harry Potter and the Half-Blood Prince, Bellatrix attempts to keep Narcissa from confiding Draco's secret mission to Snape at Spinner's End.

Snape surprises Bellatrix by replying to each of her arguments and by agreeing to create an Unbreakable Vow with Narcissa to assist Draco in his mission to kill Dumbledore.

The first chapter of Harry Potter and the Deathly Hallows implies that Voldemort is still angry with Bellatrix, as evidenced when he makes fun of the fact that her niece Tonks married werewolf Remus Lupin.

[9] In this book, Rowling reveals that Bellatrix is the guardian of Helga Hufflepuff's cup (though she is unaware that it is a Horcrux), which Voldemort has entrusted the Lestranges to keep in their Gringotts vault.

Though Voldemort apparently punishes Bellatrix and the Malfoys severely for interrupting his Elder Wand side quest only to have Potter escape and steal the cup, she nevertheless fights for her master in the Battle of Hogwarts towards the end of the novel.

[11] In this play, which takes place over 19 years after The Deathly Hallows, it is revealed that Bellatrix is the mother of the story's antagonist Delphini, whom she had with Lord Voldemort during their stay at Malfoy Manor prior to the Battle of Hogwarts.

Actress Helen McCrory was originally cast as Bellatrix in Harry Potter and the Order of the Phoenix but dropped out due to pregnancy and was replaced with Helena Bonham Carter.

[12][13][14] Coincidentally, McCrory was later cast as Bellatrix's sister Narcissa in Harry Potter and the Half-Blood Prince, during the filming of which Bonham Carter learned that she was pregnant.