Brother Matthias was originally a human called Johnathan Matthias who worked as a news anchor in America before the biological war between the people's republic of China and the Soviet Union.
As a deadly biological plague swept accross the world, Matthias made his final brodcast before he too sucumbed to the plague. Matthias and many other people were not killed by the plague but instead mutated into nocturnal albino mutants. Two years after the attack. Scarred and mad, Matthias forms a cult like group made up of the mutant survivors which he calls the "The Family"
Upon forming the Family, Matthias takes command with Brother Zachary and seeks to create a new world free of the mistakes of the past. Weapons and and forms of modern technology are banned, anything which reminds them of the past is destroyed. Being nocturnal creatures Matthias and his fellow mutants venture out of their nests and try to kill another survivor, Robert Neville.
An Army scientist called Robert Neville survived the plague and remained normal by injecting himself with a special cure. The Family see Robert as an evil reminder of their past and wish to kill him. Matthias had led several failed attacks until finally managing to capture Neville in a wine celler. The Family then take Neville to court, Matthias attended Neville's summary trial. Matthais was disgusted by Neville as he was not infected, and scheduled him for execution in Dodger Stadium.
However, at the execution, two other survivors Lisa and Dutch turned the stadium lights on, disorienting Matthias and The Family long enough for them and Neville to escape. Neville would then help cure Lisa's younger brother who almost became a mutant after being infected by the plague.
Some days later, an immunized Richie went to The Family to try and convince them to take Neville's antidote to the bio-agent. However, Matthias refused to believe that Neville would try to help The Family, accused Richie of being sent to harm them, and sentenced Richie to death. The Family then used Richie's body as bait, to lure Neville out after dark for an ambush. However, Neville was able to fend The Family off. But when Lisa succumbed to the plague, she allowed Matthias and the rest of The Family access to Neville's bunker.
When Neville returned home, he was confronted and restrained by Matthais, who forced Neville to watch as The Family set his home on fire. However, Neville was able to break free and retreat outside. Matthias stood on the balcony of the burning apartment. Neville tried to gun Matthias down, but the former's gun jammed, giving Matthias enough time to hurl a spear at Neville and mortally wound him. It is unknown what happened to Matthias next, but it is presumed that he and The Family chose to stay in Neville's burning apartment, where they perished.