He was infiltrating the Corporation for Fury, but had a breakdown and lost his memories of who he really was. Which makes him all the more tragic... Frank's really a good man, and a trusted agent of SHIELD that Fury put into an impossible situation and lost to a psychological trauma.
Interestingly, I'd say Devil-Slayer and Constrictor do know each other, through the Initiative and their mutual friend Nighthawk...
Huh. Anyone recall the issue that infiltration or his last name was revealed? tia