Brendon Doyle is a mercenary secretly working for A.I.M.'s top-secret weapons and intelligence division under the code name Mauler.
He was originally assigned by Aldrich Killian to keep Iron Man busy while they worked on perfecting the Extremis serum in time for the Mandarin debacle. Even after he was captured, Brendan chose to lead Tony astray with directions to the false operation headed by Killian's partner Kearson DeWitt before being arrested by S.H.I.E.L.D.
After the fall of SHIELD to HYDRA, Mauler was eventually freed from the Fridge by agents of the Ten Rings and recruited into their organization as an enforcer to the true Mandarin.