Harry Potter movies differs a lot from her original portrayal in J. K. Rowling's Harry Potter books. The character played by Helena Bonham Carter appeared in four film installments. Bellatrix was one of Lord Voldemort's most loyal allies, making her one of the most dangerous characters in the series.
Bellatrix was an extremely powerful witch who was a master in the Dark Arts. The member of the House of Black became a Death Eater after she graduated from Hogwarts. The sadistic follower of Lord Voldemort eventually ended up being sent away to Azkaban but later escaped during the mass break-out. Throughout the series, Bellatrix was responsible for killing major characters such as her cousin Sirius Black, Dobby the house-elf, and her niece Nymphadora Tonks. So what was different about the characters in the book series?
In the movies, Bellatrix had long, curly, black hair and pale skin. Her appearance took a hit after her time spent in Azkaban but she returned to her typical sense of fashion after she escaped. The Bellatrix in the books was described as having long, sleek hair but it never mentioned her curls. She was supposed to be tall, or at least taller than Harry.
Bellatrix was very intelligent but she often let her temper get the best of her. In the books, she seemed to have better control over her violent urges or she was at least fully aware of her actions. The Bellatrix from the movies was much more unhinged. After escaping Azkaban, she completely lost her sanity and acted out of impulse. It made more sense in the books that many of her decisions were based on her romantic feelings towards Voldemort. That message doesn't come through as clearly the movies.
As for appearances, Bellatrix first appeared in the movie, Harry Potter and the Half-Blood Prince, Bellatrix was involved in the Battle of the Astronomy Tower, but she was not present during the fight in the books. The movie also added a scene in which the Dark witch led an attack with other Death Eaters on the Burrow during Christmas break.
Bellatrix's death scene also slightly changed between the Harry Potter books and movies. Both versions revealed that she was killed by Molly Weasley during the Battle of Hogwarts. The two versions of the duel didn't exactly match up in term of spell sequence. As part of Molly's final assault on Bellatrix, she sent a spell that froze the Death Eater before hitting her with an explosion. In the books, the final blow just killed Bellatrix and she fell over. Despite the obvious difference, Bellatrix left a lasting impression in both the books and movie because of her devotion and brutality.
