This is a Joe concept character I came up with.
Jack Barnes had grown up around explosive devices his entire life. His father worked deep tunnel projects and was in charge of explosive excavations. Jack could rig explosive charges by the age of 10. He worked for his father until he was eligible to enlist in the Army and he naturally went for E.O.D. There wasn't a bomb he couldn't defuse or a situation he was afraid to put himself in. He held several records for fatest and most disarmed. Then one day in Iraq, he got to a bomb site and when he got within a few feet from the bomb, he just stopped and waited. Why should he stop this device from doing what it was meant to do. The bomb detonated. He survived the explosion and from that day forward his interest turned from stopping the bombs to surviving explosions. He began testing different suits and materials until he came up with the perfect detonation suit. This suit allowed the wearer the ability to move 3 times faster than the best EOD suit. After several of his own devices were disarmed by Jack, Firefly took an interest in his career. Once his motivation changed as Firefly knew it would, he approached Jack with a proposition. Jack took up the codename Killswitch and joined Cobra. His primary application was insuring that the bombs Firefly set would detonate and his secondary (if the Joes ever took up the offensive against Cobra) would be defusal.
In situations where an EOD specialist would be disarming one of Firefly's devices, Killswitch would approach ground-zero and make sure the bomb did what it was set to do!