Joe 90 (1968)

Joe McClaine is a 9-year-old schoolboy whose adoptive father, Professor Ian "Mac" McClaine, has developed a method of transferring specialist "brain patterns", and hence skills, knowledge and experience into his son's mind using the "BIG RAT" (which stands for Brain Impulse Galvanoscope Record And Transfer). Joe takes on the brain patterns of experts older than him and is able to become an astronaut, aquanaut, test pilot, brain surgeon, etc when needed. Joe uses these skills for the World Intelligence Network (WIN) as their most Special Agent code-named "Joe 90", where he's young age, small size and innocent appearance, allow him to carry out dangerous assignments without arousing the enemy's suspicion as no one would suspect a nine-year-old of being a secret agent.