Leon Scott Kennedy makes his first appearance as one of the protagonists of Resident Evil 2. Leon is a rookie police officer, but an expert in the art of combat, recently hired by the Raccoon Police Department (R.P.D.). When he arrives in Raccoon City, he finds the city already overrun by zombies. He teams up with Claire Redfield, and together they try to escape the city alive. He is related to Ada Wong, a woman who claimed to be looking for her missing boyfriend (John). His attempt to find an escape route leads him to an underground Umbrella lab, where he is confronted by several of Umbrella's mutated creatures.
In one of the epilogues of Resident Evil 3 it is revealed that Leon joins an agency of the United States Government. In Resident Evil: Survivor, the game's protagonist, Ark Thompson, goes to Sheena Island at Leon's request. In Resident Evil Code: Veronica, Leon is contacted by Claire when she is trapped on Rockfort Island, and Leon reveals Claire's whereabouts to her brother, Chris Redfield. Leon also appears in Resident Evil Gaiden, but with a rather overwhelming and confusing ending (this game has no bearing on the rest anyway; it's non-canon).
Leon returns as the protagonist of Resident Evil 4; where he has already become a special agent of the United States Government, and thanks to the fact of being an expert combatant, he is assigned to rescue the daughter of the newly elected president, the father of Ashley Graham, who is kidnapped and taken somewhere in Europe. His kidnappers become part of a cult known as Los Iluminados, which has taken control of the local people with parasites known as Las Plagas. And once again, Leon teams up with Ada Wong, working for Albert Wesker and Luis Sera, a former investigator for Osmund Saddler, the cult leader. Leon once again teams up with Claire Redfield in the movie Resident Evil: Degeneration to stop another T-Virus outbreak.