Jason Isaacs brought a special dark charm to the role of Lucius Malfoy in the Harry Potter films. The actor not only added his own individuality to the character but also often improvised on set, making his scenes even more memorable.
For instance, in "Harry Potter and the Chamber of Secrets," Isaacs added his own remark in a scene with Dumbledore and Harry: "Well, let us hope that Mr. Potter will always be around to save us." This phrase became a pure improv of an actor, and Daniel Radcliffe instantly supported her, replying: "Don't worry, I will be".
Isaacs did not limit himself to just learning his lines. For his role, he read all the Harry Potter books, memorizing many spells and details of the magical world. In one scene, when Lucius accidentally frees Dobby, the director asked the actor to show rage by pointing his wand at Harry and uttering a spell. Jason chose something that sounded very much like "Avada Kedavra." It's funny that this killing spell appeared in the films only in the fourth part, which added additional tension and intrigue to the scene.
These small details, like improvised lines and precise spells, helped Isaacs make Lucius Malfoy one of the most colorful and memorable antagonists of the series.