Absent-minded professor

The absent-minded professor is a stock character of popular fiction usually portrayed as an academic with important information, but whose focus on his learning leads him to ignore his surroundings.

An example of an absent-minded professor is Professor Plum from Clue, or Professor Calculus from Tintin.

Another usage of the phrase "Absent-Minded Professor" is not very uncommon in the English language. Like the phrase itself implies, it is used to describe someone who is so engrossed in his 'own world' that he fails to keep track of his surroundings. Possibly came into use because of the many professors who get so obsessed with their research that they hardly know about the 'rest of the world'.