Fardarker

Hopefully im doing things right.

First idea, not my best, but one i like despite the ridiculousness.

A containment tank (like a terrarium) housing a single butterfly, ordinary in every way except that it cannot die of old age.

This butterfly's tank is kept strictly controlled and observed because it is confirmed (through the foundations interactions with time travelers) to be the single butterfly that will one day be killed in a manner that will result in an inevitable and total apocalyptic future.

The foundation hold this butterfly knowing full well that it will one day die, but also that the longer they prevent this the longer the events can be delayed.

However, due to its extended life, its believed the butterfly has somehow come to understand its fate, and has been reported attempting suicide on several occurrences.