Half-brother and nemesis of Stewie
, unknown to other Griffin family members aside from Brian
. Bertram appears as a spermatozoan in "Emission Impossible", and as a child in "Sibling Rivalry", with the same physical appearance in both episodes. He is fathered by Peter
's sperm but was born by a lesbian couple. Peter's sperm came to create him when Peter went to have a vasectomy and goes into the donor room, spills all the jars of sperm and refills them with his own sperm.
Voiced by Wallace Shawn