It was Jean Reno's decision to play Léon as if he were "a little mentally slow" and emotionally repressed. He felt that this would make audiences accept that Léon wasn't someone who would take advantage of a vulnerable young girl. Reno claims that for Léon, the possibility of a physical relationship with Mathilda is inconceivable, so when such a relationship is discussed in the movie, Reno very much allowed Portman to be emotionally in control of the scenes. Reno stated that his rationale for agreeing to play the part was that his character was a 10 year old boy in love with a 12 year old girl, so the relationship could only ever be platonic.
This is Natalie Portman's motion picture debut. Born in 1981, she was 11 years old when she was cast.
Keith A. Glascoe later became a member of the New York Fire Department, Ladder Company 21 in Hells Kitchen. He died in the collapse of the World Trade Center towers on Sept. 11, 2001.
When the film was first tested in Los Angeles, California, USA, the version that was screened included a short scene where Mathilda asks Léon to be her lover. However, the audience became extremely uncomfortable and began to laugh nervously, completely destroying the tone of the film. The film received terrible test scores at the screening, and as such, producer Patrice Ledoux and writer/director Luc Besson decided to cut the scene for theatrical release.
Luc Besson: In the "International Cut", he is the guy shooting back at Léon and Mathilda, who Léon kills by using the grenade "ring trick".