D-Fault wears a tinfoil hat, supposedly as a defence against Claptrap assimilation. This would read well with the vacuum tubes and disc antennae applied to the head of each of the assimilated. Some people who believe in aliens wear tin-foil "caps" to allegedly prevent aliens from controlling their minds.
He wears armor and bears a shield that seems to be made from the parts and shells of claptraps.
He has a fishing rod that is attached to his back with a dead fish lying on the back of the rod. When D-Fault is killed, one can hear him say, "I'd rather be fishing..." This is a reference to the last words spoken by criminal Jimmy Glass before he was executed (intended pun) by means of electric chair in 1987.
His name refers to the fact that he and his gang reside in Dividing Faults and their being the last "default" bandits not yet transformed into bandit-traps.
D-Fault is dubbed by a woman in the Italian version of the DLC, while in the English (and perhaps in any other languages) is dubbed with a masculine voice.