What is the difference between 'he is working' and 'he has been working' and 'he had been working'?

He is working - tells us that he is at work right now. It makes no reference to the past. It only speaks of the present time. He has been working - tells us that his work is ongoing from some point in the past. He had been working - tells us only about the past. It makes no reference to what he is doing at the present time.