I'm sure someone else knows the character/actor's name, but I always smile when I recall how getting a young assistant for Columbo was met with excuses and delays . . . and finally Dog entered the picture.
The actors name is Bob Dishy. Cigargeorge makes some good points. The character did seem to be written in because he was familiar with the modern methods and technology while Columbo wasn't. In the episode Last Salute to the Commodore Columbo was assigned another young protege named Mac. Not really sure what his purpose was but it was a quirky episode anyway