Who is the Fourth DE?

[Tonks]

No: HPFGUIDX 153565

(Listening to the HBP CD over and over. It is time to take it back 
to the library
  late fees going up by the day
.   Did someone ask 
if we were addicted??)

There are 4 DE on the tower.  3 are named (Amycus and his sister 
Alecto and Greyback) and the fourth is not.  I do not see this man 
named anywhere.  Did I miss it?  I suspect that if his name was 
never mentioned, not even with Scrimgeour tells Harry that the 
ministry knows that he was on the tower because they found the DE 
stupefied, there is probably a reason.  One of those sneaky reasons 
that JKR loves to pull on us.  Does anyone remember this DE or his 
description anywhere else in the series?  He is described as 
the "brutal faced man" and he prevents Greyback from attacking DD. 

So whoever this man is the Ministry knows about him now since they 
know that he was stupefied.  How did they know?  Did they 
investigate and find him?  Or does he work for the Ministry?

Who is the fourth DE?

Tonks_op