His emotions were at a much lower level of development than Roy's, but he evidently believed in Roy's quest for more life. Leon was classified as mental level C. He did not have the speed of thought Roy had when it came to getting through a situation, resorting instead to simple violence.
Leon had cherished photographs of his friends. Unlike Rachael's false photos of her childhood, these were current photos of the only ones who meant something in his life.
After arriving on Earth with the group following their escape from an Off-world colony, Leon lodged at the Yukon Hotel on Hunterwasser street and found employment as a waste disposal engineer at the Tyrell Corporation.
Following a botched break-in to the corporation by the replicants, the police assumed that the replicants might try again by disguising themselves as Tyrell employees. Therefore, they started to question all of the workers at Tyrell's Level 9 replication center. Leon, less than a week into his employment, ended up being interviewed.
Blade Runner Dave Holden interviewed Leon, utilizing a Voight-Kampff machine. As Holden began to suspect Kowalski of being a renegade replicant, Leon brandished a gun and shot him. Leon escaped the Tyrell Corporation building and was left to roam the streets of Los Angeles freely.
Blade Runner Rick Deckard was called in to retire Leon after an encounter with Zhora. Leon spotted Deckard on the streets, following Rachael and decided to tail Deckard to surprise him and ultimately kill him.
Leon later beat Deckard severely after he witnessed him kill Zhora. Just as he was about to gouge his fingers through Deckard's eyes, he was shot by Rachael, who had picked up Deckard's gun.
Behind the scenes
According to Brion James, it was originally intended for a black actor to play the role, with Frank McRae nearly being cast. However, James was cast after Ridley Scott was impressed by his audition.
In the Marvel Comics adaptation of the film, Leon stands to fire the first shot at Holden, then shoots him again on the way out of the room. Also, Leon's death is slightly different, as he is shot in the back rather than the head.