Jason Isaacs' improvisation skills established Lucius Malfoy's cruelty early in the Harry Potter franchise. The Malfoy family is known for being heartless, pure-blooded wizards obsessed with their vile idea of purity, which leads them to side with Voldemort and become his Death Eaters. Needless to say, Lucius and Draco Malfoy never get along with Harry Potter, and they butt heads throughout the saga until their actions catch up with them.
While Lucius Malfoy's villainy is often overshadowed by the threat of characters like Severus Snape and Voldemort himself, every one of his appearances fills the room with tension. One particularly tense scene happens in Harry Potter and the Chamber of Secrets, when Harry reveals Lucius' role in the Basilisk's mystery to Dumbledore, after which Lucius storms out of Dumbledore's office. This scene heightens Lucius' hatred for Harry, but is taken to another level by Jason Isaacs' improvisation in the movie.
While exiting Dumbledore's office, Lucius turns around and kicks Dobby down a short set of steps. He then hits him with his cane and walks out the door. Lucius' shameless abuse towards Dobby perfectly showcases the contempt he has towards those he considers to be below him, and considering he doesn't attempt to hide it from Dumbledore, he clearly doesn't really respect anyone above him either. What makes this scene even more exceptional is the fact that Jason Isaacs improvised it. As he reveals in the Return to Hogwarts reunion segment "Meet the Malfoys":
We did a take, and he [Director Chris Columbus] goes "thank you, this will be all," and I swung my leg out, and I stepped down and I swung my stick, and Chris goes, "Cut! Can we clean the floor where Jason slipped, please?" And I said, "No, I didn't slip. I kicked Dobby down the stairs." And I just thought "this is going to be ridiculously good fun."
Improv Made Lucius Malfoy An Even Better Harry Potter Villain
Jason Isaacs played a huge role in Lucius Malfoy's development. Mere moments before kicking Dobby, Jason Isaacs ad-libbed the line "Let us hope that Mr. Potter will always be around to save the day", to which Daniel Radcliffe ad-libbed his response, "Don't worry, I will be." Moreover, as Jason Isaacs explains in Return to Hogwarts, his brutality in the role made Draco Malfoy actor Tom Felton feel quite intimidated during filming, though Isaacs was always quick to break character when the cameras were off.
Another memorable improvisation came when Lucius attempted to shoot a curse at Harry shortly after exiting Dumbledore's office. In between takes, Jason Isaacs forgot the name of the original spell. He instead began to utter "Avada Kedavra" before Dobby attacked Lucius. This made the scene much more terrifying than originally intended, as the killing curse is strictly reserved for life-or-death situations even by evil wizards.
Harry Potter's Malfoy family would have been very different without Jason Isaacs' contributions to Lucius Malfoy. Isaacs was the one who came up with the idea to give Lucius long blonde hair and a cobra-headed walking stick that guarded his wand — two of Lucius' trademark features that make him stand out from the rest of the Harry Potter characters. Fortunately, Jason Isaacs was one of the many perfectly-cast characters in the Harry Potter movie franchise, and his acting skills added extra layers to a villain that may not have been as unique had another actor taken the role.