I've been reading the B.P.R.D: Plague of Frogs Volume 2 TPB collection and had noticed this was included in a file that Johann Kraus was looking through in B.P.R.D.: The Dead #3:


There was also this page showing the Zinco Corporation private office of Landis Pope in B.P.R.D.: The Black Flame #2 (October 2005)

If you notice, the bottom left-hand corner panel seems to show what may have been a metal collar that could have belonged to the Steel Hawk.

Then, in Sledgehammer 44: Lightning War (2013-2014), there is a character referred to as "Herr Bergen" that comicvine seems to identify as the Steel Hawk.


Are there other appearances for this character?
Comicvine also seems to list an appearance in B.P.R.D.: The Black Goddess #1, but I haven't read that story yet.