Numbuh 5's Brother is the son of Dr. Lincoln and Mrs. Lincoln as well as the older brother of Abby and Cree Lincoln. He was never seen in the series and was only mentioned in Operation: D.I.A.P.E.R. by Abby. He has no known name and it is mentioned that he has children. He is also the reason that Abby knows so much about babies and how to take care of them.