Blaine was once a member of Team Rocket, joining due to his passion for science. He conducted experiments on some of Red's future Pokémon, including Gyarados and Eevee. However, after learning about Red's confrontations with Team Rocket, such as protecting Mew from them, Blaine left the organization, seeking to atone for his past actions. When Red arrived at Cinnabar Island, Blaine was under attack by Team Rocket members and their newly captured Moltres, which was on loan from Sabrina.
Blaine had his Rapidash carry Red to his Pokémon Lab. In return, Blaine used Red's Gyarados to fend off Moltres, allowing Red to revive an Aerodactyl from a fossil. Aerodactyl played a crucial role in rescuing Blaine and defeating Moltres.
Later, Blaine requested Red's help in Cerulean Cave. While working under Team Rocket, Blaine combined some of Mew's DNA with his own to create a hybrid Pokémon named Mewtwo. Part of Blaine's hand became infected with Mewtwo's DNA, enabling him to track the synthetic Pokémon. This led Team Rocket to attempt abducting Blaine to uncover Mewtwo's location. Using the Master Ball, Red managed to capture Mewtwo for Blaine.
The psychic connection between Mewtwo and Blaine imposed limitations on both. If they were separated for too long, both would start feeling ill. For several years, Blaine worked tirelessly to find a way to sever the bond without harming either of them.
During the Cerise Island incident, Sabrina's Spoons of Destiny paired Blaine and Yellow together to fight against the Elite Four. They confronted Lance but were ultimately defeated due to the strong bond between Mewtwo and Blaine, leaving Yellow to face Lance alone.
In Johto, during the Mask of Ice's plot, Entei chose Blaine as its partner. The healing power of Entei's flames finally severed the link between Mewtwo and Blaine, allowing them to live independently.
Although he is generally serious, Blaine also has his humorous moments, like when his moustache got burnt during training, forcing him to use fake ones. Sometimes, he uses riddles to lighten up tense situations.
