On the Buses Wiki

Jack Harper (Bob Grant) is one of the main characters of the show who appears in most episodes of the series.

One episode shows Jack living next door to the Butler residence after Stan leaves.

Another episode show Jack as inspector alongside Inspector Blake and soon turns into 'Hitler mark 2'

Jack is evidently successful with Women and attempts to teach Stan all the tricks of the trade. In later series Grant and Stephen Lewis wrote a number of episodes together.