US /ˈiən/
・UK /'i:ən/
These prokaryotes probably made their grand entrance between 3.9 and 3.5 billion years ago, during what is known as the Archaean Eon.
An eon, as you might expect, takes freakin' forever.
Still with no past, no ties to any planet in particular, and a ticking Eon Bomb of unknown purpose in their body, the Trailblazer doesn't really have anything except that singular goal of reaching the end of their story to guide them.
Now this is just speculation on my part, but the Astral Express was created by the Eon Akavili, and Akavili's origin planet is known as Pagana.
The Eon wanted to build a wall,
The Eon wanted to build a wall, and
That tenebrousness was indeed a positive quality, for it obscured such parts of the inner walls as ought to have been revealed and actually burst forth like smoke from its eon-long imprisonment, visibly darkening the sun as it slunk away into the shrunken and gibbous sky on flapping, membranous wings.
The actual word being used is "eon," which means age.