Mathilda is a central character in the 1994 action thriller film "The Professional." She is portrayed by Natalie Portman in her film debut.

Mathilda is a 12-year-old girl who is orphaned when her family is killed by corrupt DEA agents. She seeks refuge with her reclusive neighbor, Leon (Jean Reno), who is a professional hitman. Mathilda convinces Leon to take her in and teach her how to be a "cleaner" like him, hoping to get revenge on the corrupt agents who killed her family.

Mathilda is a complex character, struggling with the loss of her family and her desire for revenge. She forms a close bond with Leon, who becomes a surrogate father figure to her. However, their relationship is complicated by their shared involvement in the world of organized crime and violence.

Portman's performance as Mathilda was widely praised, with many critics noting her emotional depth and nuanced portrayal of a young girl grappling with trauma and violence. The character has since become a cult favorite and is considered one of the most memorable child characters in cinema history.