He is a relatively short middle-aged man with brown hair and a thin toothbrush mustache. He wears a beige safari helmet with a dark-brown band around it. His formal attire consists of a white shirt with bow tie under a black jacket with yellow shoulder pads. He also wears thick black spectacles at all times.
Brief comes across as a kind individual but his stay at the 'vacation' island has clearly had an effect on him: he seems quite lonely with the loss of his crew and asked Luffy to join him several times, but with no success. He is also clearly compassionate and friendly as, despite these refusals, he still helps Luffy through his despair and then aids him in taking down the Baron.
Not much is known about the Mustache Pirates beyond that they were very close and not against goofiness on occasion (if the call-sign is any indication). Brief seems to have had a very positive relationship with them and misses them greatly, but not so much that he will not befriend any others.
As a captain of a crew of pirates, it can be assumed that Brief possessed a reasonable amount of fighting skill, or at least leadership skill. He is also quite adept at the construction of tunneling passageways through the ground.
He was an unofficial occupant on Omatsuri Island, first seen spying on the Straw Hats during the "Goldfish Dipping" game. He later met up with Luffy and asked him to join his crew called the Mustache Pirates, also warning Luffy to be wary of the Baron. He later saved Luffy from being captured by the Baron during the "Shooting" game, and again when the Baron was on the verge of killing Luffy.
It is later revealed that his Mustache crew fell victim to Lily, and he begged the Baron to spare his life. However, he refused to let it happen to Luffy's crew and helped Luffy by first snapping him out of his despair when he believed his crew dead, and then distracting the Baron while Luffy got close to the monstrous Lily carnation.