The youngest of Phlox's children, who grew up to embrace the old Denobulan hatred of the Antarans and has not spoken to his father for years.
Mettus is never seen, but he is central to The Breach. When an injured Antaran named Hudak refuses to be treated by a Denobulan, Phlox is forced to talk about the long history of war between their peoples and about the prejudice he was himself raised with.
Phlox explains that he tried to bring up his five children free of that hatred, taking them to see for themselves that the old stories were distortions. With Mettus it did not work: the young man fell in with people who kept the old enmity alive, and father and son have been out of contact for roughly a decade.
His account persuades Hudak to accept surgery. At the end of the episode Phlox sits down to write to Mettus, hoping to reopen the conversation.