10 Family Guy Characters Killed Off For Good
3. Bertram
Stewie Griffin has never been faced with a more worthy opponent than Bertram, his paternal half-brother who had previously formed an alliance with Stewie in Lois's womb.
The character, voiced hilariously by Wallace Shawn, is Stewie's equal in almost every way: intelligence, psychopathy, and technical proficiency. When he is finally born, Bertram wages war on Stewie over ownership of a Quahog playground. After this, their rivalry grows fierce, and looks set to be quite the recurring thing in later series.
Weirdly, though, that's not the case. Bertram's final appearance is in the season nine episode, 'The Big Bang Theory', as he travels back in time to kill Leonardo da Vinci, Stewie's ancestor, and thereby stop Stewie from ever having been born.
He succeeds in doing away with da Vinci, but Stewie is able to prevent his erasure by taking the painter and inventor's place in Renaissance Italy. And to do this, he shoots Bertram in the head with a crossbow, killing him instantly.