The Grandfather of All Knowledge is a deity-like character mentioned by Dexter which he appears to revere and was first mentioned during a dream in the episode Dream Machine. According to his name, he appears to be omniscient.

In his dream, Dexter went to visit the Grandfather of All Knowledge atop his giant chair on a mountain, but when he turned around it was Dee Dee who proclaimed herself to be the Grandfather of All Knowledge. Dexter then expressed that this could not be true and he quickly realized that he was having a nightmare.

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