Frank Castle worked for S.H.I.E.L.D. and was given some of the Super-Soldier Serum by "President Rogers". He was sent out to kill super-heroes. During their attack on Spider-Man, Frank did not like Clinton Barton murdering Parker's aunt and Uncle as well.
Much later he was sent out to capture Namor, but Namor escaped and fled to the Arctic. Here he was able to defeat Castle, so Castle was given a suit of armor developed by Tony Stark, donning the identity of Iron Man. He used it to capture Namor, who had just found the real Captain America. After Captain America thawed, Frank turned on his fellow S.H.I.E.L.D. and joined Cap's new Avengers.
The author marked this model as their own original creation.