Lucas Morrissey is one of the Morrissey brothers; he and his brother are introduced in Maximum Ride Forever. They are boy geniuses, microbiologists who made breakthroughs in the field while they were still in high school. There was a TV special on them which Angel saw.
The Remedy recruited them to work on an antidote to the H8E virus, which they gave to their sister Olivia; tragically, she died anyway. Afterwards, realizing that the Remedy was evil, they burned down the lab and went on the run.
Angel found them hiding in a boxcar, pretending to be brainwashed by the Doomsday Group. She convinced them to come to Russia as part of her army.
During the nuclear winter, the Morrisseys replicated the antidote to the virus, using Fang's DNA.
The Morrissey brothers are black. Lucas is older by two years, as well as taller and stronger-looking.