"The Diary" is the thirtieth episode of the sixth season of the American animated television series Adventure Time. In the episode, Jake's son T.V. finds an old diary, which revives a decades-old mystery. It was written by Canadian illustrator Jillian Tamaki, her second episode on the show after "Astral Plane". The episode was broadcast on Cartoon Network on February 26, 2015. Writers of Wired and The A.V. Club praised Tamaki for the way she wrote the episode as well as the visuals overall.