absent-minded professor

noun2

1. •
   A stereotypical fictional character whose focus on academic matters leads them to ignore or forget their surroundings.

   • Professor Oak, the world's leading Pokémon expert, is at once a genius and a bumbling, absent-minded professor — 2009
2. •
   A person who tends to be oblivious to reality.

   • Snapshot: Jimmy, a third-grader, is an absent-minded professor before his time. He forgets everything, from his lunch box in the morning, to his raincoat — 1997