When you are played in a docu-drama by Benedict Cumberbatch I think you can say you have become well known. I watch a lot of American news and financial programmes. I have heard DCs name mentioned reasonably often in them, I would not be surprised if viewers of these programmes know him far better than most of our cabinet ministers.
He played a major part in winning the Brexit referendum and also winning the GE, he is undoubtedly a smart individual but as TM said he broke the spirit of the law and if he had 1/10th the honor of someone like Lord Carrington (credit to flecc for reminding me of him) he would have resigned weeks ago.
Cabinet ministers say off the record that he has more power than they do, he controls access to the PM, if they want to see Boris they have to go through him. How many other advisors have been given their own press conference in No10s rose garden. Its amazing the power this unelected official has, I wonder sometimes has he got some dirt on Boris that he is holding over him.
Or (more likely) is Boris absolutely reliant on him because DC is the only person in Government who actually has some idea of what he is trying to achieve. Boris I think is just trying to get through the next few years without making too much of a mess of things, hoping to lie and bluff his way thorough. Then bow out before the next election and cash in on being an ex PM.