The episode "The Why of Fry" explains that Fry’s cryonic freezing was not an accident but a plan orchestrated by the Nibblonians to ensure he would be in the future to save the universe.
In "Leela's Homeworld," it is revealed that Leela is not an alien but a mutant whose parents gave her up to the Surface World orphanage to provide her with a better life. Futurama - Season 4
While it is the fourth production season, Fox broadcast these episodes across its fourth and fifth seasons. The episode "The Why of Fry" explains that
Season 4 was initially intended to be the series finale following Fox's decision to cancel the show due to low confidence and erratic scheduling. Consequently, the season contains several "landmark" episodes that resolve long-standing mysteries, such as Leela’s true origin and Fry's destiny as "the chosen one". Season 4 was initially intended to be the