Flashbang is a NPC ally you can find during the mission Break Goldbrickers out of Wyvern hideout from Golden Roller (CoV, levels 15 - 20). He's the mission objective, and must be freed from Wyvern squads.
Once free, he will follow you and will attack any Wyvern mercenary in his aggro range.
There are two other Gold Brickers prisoners, two Bombardiers in this mission. While you don't seem to need to free them, I'd advice to do it. Their debuffs stock quickly, and the firepower of the three combined is surprisingly high: nothing was lasting much in front of them.
During my mission, Flashbang had slightly less hit points that a Lieutenant of the same level. He was probably a watered-down Boss class ally. He has a faction of Gold Brickers. Expect several ambushes from Wyvern once you free him.
Since he's the mission objective, he must be escorted to the mission exit and must survive if you want the mission to be succesful.
During the mission he will say the following:
Flashbang: Alright! Let's get outta here!
At the mission exit:
Flashbang: Nice work, Villain.
During my mission, he used the Boomer typical attacks: