Dr. Gordon is a character of the day who appeared in Caterpie's Big Dilemma.
A scientist, Dr. Gordon lives near Saffron City with his student, Xander. The doctor's specialty is making inventions, and his lab is filled with a lot of them. Among them, there is a machine that enables him to use Alakazam's Future Sight in order to predict the future, and a Machoke costume that allows him to run quickly.
One of his inventions, the Mystery Candy Complete, is something he accidentally created. After Xander's Caterpie accidentally ate some, he began panicking, because he hadn't tested the candy yet. The little Pokémon immediately grew, and broke out of the lab.
Seeing this, Team Rocket decided to kidnap him so they could make him invent objects for them. Xander's Caterpie, meanwhile, had fully evolved into a Butterfree, which he and Ash used to save the doctor. After Butterfree shrunk back to its normal size, the doctor promised the city's Officer Jenny that he wouldn't perform any experiments like that again. Bulbapedia