Bellatrix Lestrange

"Shut your mouth! You dare speak his name with your unworthy lips, you dare besmirch it with your half-blood's tongue, you dare —"

- Bellatrix Lestrange to Harry Potter Bellatrix Lestrange is the secondary antagonist of the Harry Potter franchise. She is one of the most powerful dark witches in her time and the one to perform the Cruciatus Curse on Neville Longbottom's parents. Bellatrix is Voldemort's most loyal and trusted follower and former love and the mother of their daughter Delphini (who is the main antagonist of Harry Potter and the Cursed Child).

Background
Bellatrix Black was the daughter of Cygnus Black III and Druella Black (nee Rosier). She had two sisters: Narcissa and Andromeda and had a fairly strained relationship with her cousin, Sirius Black. At eleven, Bella began attending school at Hogwarts and was sorted into Slytherin. Bellatrix joined the Death Eaters after graduating from Hogwarts. She participated in the torture of Frank and Alice Longbottom.

Personality
Bellatrix is cruel, evil and vindictive and quite cruel. She is known to be quite psychotic, as she always laughs. She is very loyal to Voldemort, her master, and also kills in his name. She had an obsessive love for her master, and he even had a sexual relationship with her that caused the birth of her daughter, Delphini.

The Goblet of Fire
Bellatrix appears in the fourth novel, where she appears with her husband and brother-in-law and fellow Death Eater Barty Crouch, Jr. Their trial appears, where Harry witnesses how she and her family are imprisoned due to their involvement in the torture curse on Frank and Alice Longbottom.

The Deathly Hallows
During the final battle, Bellatrix murdered her disowned niece, Nymphadora Tonks. She is finally killed by Molly Weasley after she attempts going after Ginny.

Harry Potter film series
In the Harry Potter films, Bellatrix was portrayed by Helena Bonham Carter. She was ignored in The Goblet of Fire, as are her brother-in-law Rabastan and husband.

Trivia

 * Bellatrix is one of the most evil characters in the Harry Potter franchise, along with Voldemort and Dolores Umbridge, being ultimately pure evil.