Answer:
Mailman
Step-by-step explanation:
Mailman comes everyday to delivery mails. He drives a USPS van and wears a USPS uniform. He is a good worker as he works whether it is raining or cold outside.
The idea for a plot is that he always rings the bell twice. Not once, not thrice but always twice. I notice that one day and get curious. I find out that there is a reason he is doing it.
It sounds like an interesting investigative play.