In season 5 of Lost, one of the biggest mysteries revolved around the character Jeremy Bentham and the reason behind his presence. Throughout the series, Lost established itself as a mysterious puzzle, keeping fans guessing with various plot threads. Jeremy Bentham's identity was first introduced in season 3, but it wasn't until season 4 that his shocking identity was revealed.

It turned out that Jeremy Bentham was actually John Locke, a character who had played a significant role in the series. In season 5, Locke found himself trapped in a well after a time flash severed his rope. He was then tasked with reuniting the island's Oceanic Six and convincing them to return.

His journey as Jeremy Bentham was explored in episode 7 of season 5.

Desperate to get the Oceanic Six back to the island, Locke attempted to end his own life but was stopped by Ben Linus. In a shocking turn of events, Ben killed Locke and staged his death to look like suicide, using the grief to motivate the Oceanic Six to return.

The reason behind Ben's actions finally became clear in season 6. Ben, who had always been covetous of power and status, was jealous of Locke's standing among the Others.

Killing Locke allowed Ben to regain control and recreate the original plane crash to fulfill their fated events.

In conclusion, the mystery of Jeremy Bentham's identity in Lost was revealed to be John Locke, and the reason behind Ben's decision to kill him was driven by jealousy and the desire for power. This storyline added to the overall complexity of the show and kept viewers engaged until the very end.